Novametrix 2001 Service Manual
Service Manual
Pulse Oximeter
Model 2001
April 25, 2001
Catalog Number 9400-90-01
Novametrix Medical Systems Inc. Wallingford, Connecticut, U.S.A. 06492.
Copyright 2000−2001. All rights reserved. No part of this manual may be reproduced
without the written permission of Novametrix Medical Systems Inc.
About This Manual
About This Manual
Revision History
This manual is intended for use by technical personnel for servicing the Model 2001.
Refer to the Model 2001 User’s Manual (Cat. No. 9400-23) for detailed information on
normal operation.
Novametrix is a registered trademark and MARSpO
and SuperBright are trademarks of Novametrix Medical Systems Inc.
Copyright 2000 Novametrix Medical Systems Inc. This document contains information
which is proprietary and the property of Novametrix Medical Systems Inc., and may not
be reproduced, stored in a retrieval system, translated, transcribed or transmitted in
any form, or by any means, without prior explicit written permission from Novametrix
Medical Systems Inc.
The Model 2001 monitor and its sensors and accessories are covered by the following
US patents: 5,190,038 5,398,680 5,448,991 5,820,550 5,999,834 5,891,026 6,073,038
6,149,481. Other patents pending.
7-Nov-00 Release
25-Apr-01 Rev 01, R-N905
, Y-Sensor, Oxysnap, NovaCARD
2
Declaration of Conformity with European Union Directives
The authorized representative for Novametrix Equipment is:
European Compliance Services Limited
Oakdene House
Oak Road
Watchfield
Swindon, Wilts SN6 8TD
UK
Manufacturing, Quality and Safety
Novametrix manufacturing facility is certified to ISO 9001 and EN46001 (MDD93/42/
EEC Annex II). Novametrix Medical Systems Inc. products bear the “CE 0086” mark.
The product is certified by Underwriter’s Laboratories (UL) to bear the UL mark; and
tested by TUV Rheinland to IEC601-1 / EN60601-1.
Rev. 01 Model 2001 Service Manual iii
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Manufacturing, Quality and Safety
iv Model 2001 Service Manual Rev. 01
Contents
Patient Safety ................................................................................................................1
Warnings .....................................................................................................................1
Cautions ......................................................................................................................2
Introduction ...................................................................................................................5
SpO2 Principles of Operation ......................................................................................5
Indications and Usage .................................................................................................6
Symbols .......................................................................................................................6
Illustrations ...................................................................................................................7
Front Panel ..................................................................................................................7
Rear and Top Panel ....................................................................................................8
Theory of Operation ....................................................................................................9
2726 Power Supply Board ...........................................................................................9
AC Mains and Battery Operation Overview .......................................................9
AC Mains Operation ........................................................................................10
Battery Operation .............................................................................................10
2775 Main Board .......................................................................................................10
Power On/Off Control Circuitry ........................................................................11
Power Supplies ................................................................................................11
Voltage References .........................................................................................12
Preserving RAM and Real Time Clock Data ....................................................12
Low Battery Voltage Shutdown ........................................................................13
Timing Sequencer ............................................................................................13
Data Sampling Controller .................................................................................13
Sensor LED Drive Circuits ...............................................................................14
Sensor Photodiode Return Path ......................................................................15
Calibrating the 20-Bit Analog-to-Digital Converters .........................................15
20-Bit Analog-to-Digital Conversion .................................................................16
Sensor Status Decoding and Conversion ........................................................17
Sensor Status Parameters ...............................................................................17
Microprocessor ................................................................................................18
Memory ............................................................................................................18
Real Time Clock (RTC) ....................................................................................19
Sound generator ..............................................................................................19
Keypanel Interface ...........................................................................................19
Display Interface ..............................................................................................20
I/O Device Controller .......................................................................................20
Watchdog Timer ..............................................................................................21
Serial I/O Controller .........................................................................................21
RS232 Serial Communication ..........................................................................22
2776 DSP Module .....................................................................................................23
Power Supply & Supervisory Circuits ..............................................................23
UART and Level Shifting Circuitry ...................................................................23
DSP Processor ................................................................................................24
Memory and Programmable Logic Device (PLD) ............................................24
Rev. 01 Model 2001 Service Manual v
JTAG Emulation Interface ............................................................................... 24
Functional Test ........................................................................................................... 25
Equipment Required ................................................................................................. 25
Procedure ................................................................................................................. 25
Special Power Up Functions ..................................................................................... 26
Accuracy Test ............................................................................................................. 27
Equipment Required ................................................................................................. 27
Procedure ................................................................................................................. 27
Electronic Tests ......................................................................................................... 29
Equipment Required ................................................................................................. 29
Procedure ................................................................................................................. 29
Safety Testing ........................................................................................................... 33
Maintenance ............................................................................................................... 35
General ..................................................................................................................... 35
Maintenance Schedules ............................................................................................ 35
Cleaning and Sterilization ......................................................................................... 35
Model 2001 Monitor ........................................................................................ 36
SpO
Finger Sensor ........................................................................................ 36
2
SpO
Y-Sensor ............................................................................................... 36
2
SpO
Tapes and Foam Wraps ........................................................................ 36
2
Ear Clip ........................................................................................................... 36
Battery Life and Maintenance ................................................................................... 37
Mains Voltage Configuration ..................................................................................... 37
Fuse Replacement .......................................................................................... 37
Changing the Mains Voltage Setting ............................................................... 38
Assembly Exchanges ................................................................................................ 40
Changing System Software ...................................................................................... 42
Troubleshooting ......................................................................................................... 43
Fault and Error Condition Messages ............................................................... 43
........................................................................................................................ 43
Miscellaneous Messages ................................................................................ 44
Specifications ............................................................................................................. 45
General ..................................................................................................................... 45
Oxygen Saturation (SpO2) Section ........................................................................... 45
Pulse Rate Section ................................................................................................... 45
General Specifications .............................................................................................. 46
Additional Features ................................................................................................... 46
Accessories ................................................................................................................ 47
Model 2001 Pulse Oximeter ...................................................................................... 47
Parts Lists ................................................................................................................... 51
Schematic and Assembly Drawings ......................................................................... 61
vi Model 2001 Service Manual Rev. 01
Section 1 Patient Safety
The SpO2 input for the Model 2001 Pulse Oximeter is electrically isolated. Patient leakage
current flowing from the instrument to ground is limited to less than 25 mA at 120 VAC, 60 Hz.
Patient isolation is greater than 10 MΩ, 4000 VAC rms at 60 Hz. The Model 2001 is Year 2000
compliant.
For maximum patient and operator safety, the following are recommended:
• Failure of Operation: If the monitor fails to respond as described, do not use it until the
situation has been corrected by qualified personnel.
• Keep Model 2001 and its accessories clean.
• Do not operate Model 2001 when it is wet due to spills or condensation.
• Do not operate Model 2001 if it appears to have been dropped or damaged.
• Connect the line cord only to a grounded hospital-grade outlet. Model 2001 should be
connected to the same electrical circuit as other equipment in use on the patient. Outlets
on the same circuit can be identified by the hospital’s engineering department.
• Care should be exercised to assure continued peripheral perfusion distal to the SpO
sensor site after application.
• Components of this product and its associated accessories which may have patient
contact are free of latex.
• The Model 2001 contains no user serviceable parts. Refer servicing to qualified service
personnel.
2
Warnings
WARNING
!
• Explosion Hazard: Do NOT use Model 2001 in the presence of flammable anesthetics.
• Electrical Shock Hazard: Always turn Model 2001 off and remove line cord before
• Do not operate Model 2001 when it is wet due to spills or condensation.
• Do not operate Model 2001 if it appears to have been dropped or damaged.
• Patient Safety: Extreme care should be exercised with neonates to assure continued
• Failure of Operation: If the monitor fails to respond as described, do not use it until the
• Patient Safety: Care should be exercised to assure continued peripheral perfusion distal
Rev. 01 Model 2001 Service Manual 1
Indicates a potentially harmful condition that can lead to personal injury
Use of this instrument in such an environment may present an explosion hazard.
cleaning it. Do NOT use a damaged sensor or one with exposed electrical contacts. Refer
servicing to qualified service personnel.
circulation distal to the sensor site after application.
situation has been corrected by qualified personnel.
to the SpO
sensor site after application.
2
Section 1 Patient Safety Cautions
• Data Validity: As with all pulse oximeters, inaccurate SpO2 and Pulse Rate values may
be caused by:
• Incorrect application or use of a sensor
• Significant levels of dysfunctional hemoglobin such as carboxyhemoglobin or
methemoglobin
• Significant levels of indocyanine green, methylene blue, or other intravascular
dyes
• Exposure to excessive illumination such as surgical lamps—especially ones with
a xenon light source, or direct sunlight
• Excessive patient movement.
• Venous pulsations.
• Electrosurgical interference
• Data Validity: The Pulse Oximeter should not be used as a substitute for an ECG monitor.
The oximeter’s Pulse Rate display reflects the pulsatile flow found at the patient extremity
connected to the sensor. This rate can be affected by many factors and may occasionally
be “frozen.”
• Do NOT attach an SpO
processed when the cuff is inflated. Attach the sensor to the limb opposite to the site used
for the blood pressure cuff.
• Do NOT apply Y-Sensor™ tapes or wraps so tightly that the circulation is restricted.
Inspect site often for adequate circulation - at least once every four hours. When applying
sensors take note of the patient’s physiological condition. For example, burn patients may
exhibit more sensitivity to heat and pressure and therefore additional consideration such
as more frequent site checks may be appropriate.
• Do not position the sensor cable in any manner that may cause entanglement or
strangulation.
• The Model 2001 has no protection against the ingress of water.
sensor distal to a blood pressure cuff. Valid data CANNOT be
2
Cautions
CAUTION
Indicates a condition that may lead to equipment damage or malfunction.
• Do not operate Model 2001 when it is wet due to spills or condensation.
• Do not operate Model 2001 if it appears to have been dropped or damaged.
• Never sterilize or immerse the monitor in liquids.
• Do not sterilize or immerse sensors except as directed in this manual.
• No tension should be applied to any sensor cable.
• Overstretching the pulse oximeter finger sensor can damage the sensor and potentially
affect pulse oximeter readings. Do not stretch the finger sensor open beyond the limit for
which it was designed. Overstretching can be prevented: avoid opening the sensor by
any means other than squeezing the grips; Do NOT force the sensor onto large objects
such as the bed rail.
• Do not store the monitor or sensors at temperatures less than 14× F (-10× C) or greater
than 131× F (55× C), 10-95% R.H. non-condensing.
• Do not operate the monitor or sensors at temperatures less than 50× F (10× C) or greater
than 104× F (40× C), 0-90% R.H. non-condensing.
2 Model 2001 Service Manual Rev. 01
Cautions Section 1 Patient Safety
• Where electromagnetic devices (i.e. electrocautery) are used, patient monitoring may be
interrupted due to electromagnetic interference. Electromagnetic fields up to 3V/m will
not adversely affect system performance.
• Federal (U.S.A.) law restricts this device to sale, distribution, or use by or on the order of
a licensed medical practitioner.
Rev. 01 Model 2001 Service Manual 3
Section 1 Patient Safety Cautions
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4 Model 2001 Service Manual Rev. 01
Section 2 Introduction
This manual describes the use and operation of the Model 2001 Pulse Oximeter Monitor from
Novametrix Medical Systems Inc.
Model 2001 is a lightweight, easy to use, pulse oximeter designed to be used in a variety of
clinical settings. It provides reliable measurement, display and alerts for functional pulsatile
oxygen saturation (SpO
voltage) or from its rechargeable internal battery.
Numerical and waveform information is presented on a bright Cold Cathode Display (CCD) with
user adjustable contrast to optimize viewing angles. A simple menu system allows user
selection of measurement and display options. Alerts are menu programmable or automatic.
Numerical and plethysmogram displays are continually updated. Presence of a pulse is
indicated audibly by a user selectable “beep”.
Separate 24 hour trends for SpO
trend “events” and audible alarm status (Audio Off) are stored in trend memory.
The monitor is equipped with an RS232 serial output port for easy interfacing to external
equipment. An optional Analog Output module provides analog outputs.
Per requirements of IEC 601-1, the Model 2001 is classified as class II equipment, with type BF
applied part, and an enclosure protection rating of IPX0. The Model 2001 is Year 2000
compliant.
) and pulse rate. The monitor can be powered from the AC Mains (line
2
and pulse rate are updated every 8 seconds. In addition,
2
SpO2 Principles of Operation
Model 2001 measures oxygen saturation and pulse rate with sensors that contain red and
infrared light sources, called LEDs. Since oxygen saturated blood absorbs different amounts of
light at each wavelength (red and infrared) as compared to unsaturated blood, the amount of
light absorbed by the blood in each pulse can be used to calculate oxygen saturation.
The light energy from red (660 nm) and infrared (940 nm) LEDs is beamed through a sample
cell, such as a pulsating vascular bed—the patient’s finger or toe, for example. The remaining
light energy not absorbed by the sample cell reaches a light receptor, called a photodiode, on
the opposing side of the sensor. The data received at the photodiode is sent back to the monitor
where it is split into its red and infrared components, digitized, processed by a microprocessor
chip, and finally displayed as a numerical value for oxygen saturation and a plethysmogram.
Rev. 01 Model 2001 Service Manual 5
Section 2 Introduction Indications and Usage
Model 2001 is calibrated to display “functional” saturation. This differs from the “fractional”
saturation value displayed by most co-oximeters.
Equation 1. Functional
Saturation Calculation
Indications and Usage
HbO
Functional Saturation =
HbO
= Fractional Hemoglobin
2
COHb = Carboxyhemoglobin
METHb = Methemoglobin
Functional saturation represents the amount of oxyhemoglobin as a percentage of the
hemoglobin that can be oxygenated. Dysfunctional hemoglobins (COHb and METHb) are not
included in the measurement of functional saturation.
Pulse Rate is calculated by measuring the time interval between the peaks of the infrared light
waveform. The inverse of this measurement is displayed as pulse rate.
Model 2001 must be used in conjunction with SuperBright™ saturation sensors. (An CHECK
SENSOR SITE display message indicates a non-SuperBright™ Sensor may be in use.)
The Model 2001 Pulse Oximeter Monitor is intended to be used for monitoring oxygen
saturation and pulse rate in all critical monitoring environments including ventilatory support
and anesthesia. Model 2001 is designed to monitor all patient areas including adult, pediatric
and neonatal.
100 - (COHb + METHb)
2
Symbols
Symbol Description
!
Pb
Patient Isolation
Identifies patient isolation connection as type BF.
Attention
Consult manual for detailed information.
Separate collection
Ensure that spent batteries are collected separately when
disposed of. Found on the internal battery. Refer to qualified service personnel when battery replacement is
required.
Recyclable item
Found on the internal battery. Refer to qualified service
personnel when battery replacement is required.
Indicates heavy metal content, specifically lead. Found
on the internal battery and monitor enclosure. Refer to
qualified service personnel when battery replacement is
required.
6 Model 2001 Service Manual Rev. 01
Section 3 Illustrations
Front Panel
1 17
8765432
1. Alert Indicator. Flashes (red) when
an alert/alarm occurs. Continues to
flash until condition corrected and
ALERT RESET is pressed.
2.
3. Low Battery Indicator. Illuminates
4. AC Power Indicator. Illuminates
5. Two Minute Silence Indicator.
6.
7. Audio Off Indicator. Flashes
POWER key. Press to turn on
monitor.
(red) if monitor powered from battery.
Flashes to warn of low battery voltage
condition.
(green) if monitor is connected to AC
(Mains) and the rear panel power
switch is set to “|”.
Illuminates (yellow) when the
AUDIO key is pressed. Alarms silenced
for two minutes.
AUDIO key. Press and release to
turn on/off the two minute silence
function. Press and hold to enable the
Audio Off feature (unless disabled via
Options Menu). Press and release to
disable Audio Off.
(yellow) as a warning that the audible
alarms are disabled.
1516
911
8.
9.
10. Kickstand and bedrail hanger.
11.
12. Red Alert Bar. Flashes (red) when an
13. SpO
14. Contrast key. Press to adjust
15. Waveform or trend data displayed
16. Menu Display. Softkey functions and
17. Parameter Numerical Displays.
ALERT RESET key. Press to
disable active alert indicators. Alerts
will reactivate if alert condition still
exists.
SOFTKEYS. Press software keys 1-
5
(left to right) to initiate action listed
above each key.
EVENT key. Press to place an
“event marker” into the trend.
alert/alarm occurs. Continues to flash
until condition corrected and
ALERT RESET is pressed.
Sensor Input Connector.
2
display for optimum viewing.
here.
menu messages displayed here.
Numerical displays and alert limit
settings for measured parameters
displayed here. Also display units and
special display options noted here.
14
13
1210
Rev. 01 Model 2001 Service Manual 7
Section 3 Illustrations Rear and Top Panel
Rear and Top Panel
123456 7
10
8
9
1. Ground symbol: Equipotentiality.
Connection to monitor’s chassis.
2. Line Cord Clip: This clip can be set
around the line cord strain relief so that
the cord cannot be pulled out of the
connector.
3. Line Cord Connector: The AC (Mains)
line cord attaches to the monitor here.
4. AC Mains Power Switch: With switch in
“O” position, AC Mains voltage does not
enter monitor. With switch in “|” position,
AC Mains voltage allowed into monitor
to power unit and/or charge internal
battery.
5. Fuse Compartment: The AC (Mains)
line fuse(s) are inside this compartment.
Pry open with small screwdriver.
6. AC Mains Voltage: The currently
selected AC Mains input voltage is
identified here.
11
12
7. Serial Output Connector: Serial (RS232)
data output here for use with RS232
interfaces. A female 25-pin “D”
connector serves as the interface
connector.
8. Attention: Consult manual for detailed
information.
9. Top Cover
10. Carrying Handle: Monitor carrying
handle molded into case.
11. Warning Label: Explosion and electrical
shock warnings.
12. Patient Isolation Label: The Model 2001
is Type BF equipment.
8 Model 2001 Service Manual Rev. 01
Section 4 Theory of Operation
The Model 2001 is a microprocessor based instrument that measures the clinical parameters
of oxygen saturation (SpO
controlling, collecting, conditioning and displaying patient information gathered from the
Superbright™ sensors. The theory of operation of the Model 2001 is explained in detail in the
subsections that follow. Refer to the Schematic and Assembly Drawings for further information.
2726 Power Supply Board
The 2726 Power Supply Board contains the circuitry needed to power the monitor from the AC
Mains (line voltage). The power supply board also connects to the battery and contains the
battery charging circuitry.
AC Mains and Battery Operation Overview
The Model 2001 can be powered from its internal 12 volt battery or from the AC Mains. The
green (sine wave icon) front panel indicator illuminates when the line cord is connected and the
rear panel power switch is in the “|” (On) position. This indicates that AC Mains power is
reaching the power supply, that the battery is being charged, and that if the monitor is turned
on, it is being powered from the line voltage.
If AC Mains power is removed by unplugging the line cord or setting the rear panel power switch
to the “0” (Off) position, the monitor will operate for up to four hours from its internal 12 volt leadacid battery. As the battery voltage runs low (<11.5 volts), the red battery indicator on the front
panel illuminates. At this point, the AC Mains should be reconnected to power the monitor and
charge the battery.
If the monitor continues to be powered from a battery in a low voltage situation, at approximately
11 volts, a continuous alarm sounds for thirty seconds while the Message Center displays
BATTERY EXHAUSTED CONNECT LINE CORD. If this alarm/message is ignored, the monitor
displays will shut down and the battery indicator will flash on and off about every 5 seconds. If
AC power is now restored, the monitor will re-initialize (go through the power up and self-test
routines) and resume normal operation. However, continued battery operation will eventually
activate a hardware low voltage circuit (<8.5 volts) that shuts the monitor off to prevent damage
to the battery. Once the unit is shut down with the hardware circuit, the AC Mains must be
connected and the front panel POWER key pressed before the monitor will turn back on.
) and pulse rate. The system contains all the circuitry necessary for
2
Rev. 01 Model 2001 Service Manual 9
Section 4 Theory of Operation 2775 Main Board
AC Mains Operation
The AC Mains voltage enters the monitor at the rear panel Power Entry Module (PEM). This
device contains a built in RFI power line filter, a double-pole single-throw switch that opens and
closes both AC input lines, fuses, and an input voltage selection card.
The filtered, switched and fused output of the Power Entry Module is fed to the primary coils of
the rear panel mounted system transformer, T301. The secondary output from T301 is rectified
by D1 (bridge rectifier) and filtered by C1. The loaded DC voltage at this point is approximately
20 volts.
The 20 DC volts is fed to the 2775 main board through fuse F301 to connector E302, and is
switched to the battery charging regulator IC1 (pin 5) through Q1B. Biasing for Q1B is
accomplished by C2, R1, R2, C8 and Q1A when AC power is applied. When running on battery
power Q1B is biased off by R2 and Q1A, this prevents the battery from trying to power the
battery charger regulator and IC2 that informs the monitor of the loss of AC.
The output of switching regulator IC1 pin4 is rectified and filtered by D4, C4 and L1 then fed to
the battery through current sense resistor R3 and fuse F302 to VBAT+ (J302 pin 1). The battery
float charge voltage is maintained at 13.2 volts except for fast charge which is regulated at 14.4
volts. The output is also monitored for over current conditions. These parameters are controlled
by IC3 and associated circuitry. When the battery charge current exceeds 120mA of current IC3
pin 7 goes high which biases Q2 on, this in turn shorts out R12 which affects the feedback
control (FB) to IC1 (pin 1). With R12 shorted out the control resistors R14 and R13 set the
output voltage to 14.4 volts. When the charge current lowers IC3 pin 7 goes low which biases
Q2 off, this puts R12 back into the feedback control which now consists of R12, R13 and R14
setting the voltage to 13.2 volts. When more than 600mA of current flows through R3, IC3 pin
1 shorts IC1 pin 2 to ground which shuts IC1 off until its next switching cycle, when the current
reaches a safe level IC3 pin 1 allows IC1 to remain on.
The voltage rectified by D1, D2 and filtered by C2 is fed to IC2 as VCH (Voltage Charge). The
output of this 5 volt regulator provides the LINEST (Line Status) signal to the main board at
E302 pin 3. With AC applied, LINEST is high. LINEST goes low when the AC is disconnected.
The LINEST line is also routed to the power on/off circuitry. See Power On/Off Control Circuitry
on page 3.
Battery Operation
Without AC power there will be no secondary voltage rectified by D1. Power for the monitor will
be supplied from the battery at J302 pins 1 (VBAT+) and 2 (VBAT-). The battery power will
conduct through D3 and F301 to VIN at E302 pin 1 to the 2775 main board. R2 and Q1A bias
Q1B off in this condition which prevents power from reaching IC1, IC2 and IC3. The output of
IC1 is also protected by D5 which is now reverse biased, the bridge D1 is also reverse biased
and prevents T301 from discharging the battery. With no voltage at IC2 the LINEST will be low
which indicates to the main board that there is no AC power.
2775 Main Board
The 2775 Main Board contains all the analog and digital circuitry that controls the sensor,
external communication and front panel display. The isolated power supplies, microprocessor
circuits and memory are all contained on this board as well as the communication interface to
the DSP board.
10 Model 2001 Service Manual Rev. 01
2775 Main Board Section 4 Theory of Operation
Power On/Off Control Circuitry
See page 4 of 4 on schematic.
The Model 2001 power on/off control circuitry consists of the VBACK supply (regulated by
IC12), IC10, IC11 and the POWER key.
When the battery or AC Mains is first applied to the power supply board (via VIN J102 pin 1),
VBACK goes to +5 volts, provides power to IC10 and IC11, and through the C26 and RP4 (pins
3,4) network at IC10 pin 8, sets IC10 pin 2 to a logic Low.
The ON/OFF line is brought Low each time the front panel POWER key is pressed. This sends
the output at IC11 pin10 High. This Low-to-High transition clocks the (#1) D flip-flop portion of
IC10. The Q1
key, this output toggles to the opposite level (Low or High). A High turns the Model 2001 on and
a Low shuts it off.
While the Q1
MOSFET Q8 to ground, thus causing Q8 to conduct as well. With Q8 conducting, the currently
active monitor power source-either the AC Mains derived supply or the battery supply will flow
through Q8 to the voltage input (pin 7) of the Pulse Width Modulator IC9. The output IC9 pin 6
will oscillate (at the frequency set by R13 and C15). This causes Q5 to switch on and off and
provide a path to ground through the primary coils of T1 for the supply (Mains or battery) at T1
pin 12. Current flowing in the primary is measured at IC9 pin 3 and the duty cycle of the pin 6
output will vary with the load on the transformer.
Current flow in the transformer primary induces current in the three secondary coils and creates
the 12 volt analog supplies (+V12 and -V12), +VA, the VRAWI that powers the isolated RS232
circuitry, and the +5 volt VCC supply that power the remaining circuits in the monitor. The Model
2001 turns on. The +V12 and -V12 supplies are rectified and filtered by D2, D4, C10, C11, C12
and C13. The +V12 is regulated by IC7 and the -V12 by IC8. The Vcc supply is rectified by D3,
filtered by L1, C9 and C20 and fused at F1, and in addition, a feedback loop to IC9 contains
VR1 which is factory adjusted to produce a +5.00 volt ± 0.05 volt VCC supply (measured under
load).
Once the monitor powers up, a SYNC signal toggles Q9 on and off causing a timing pulse to
be transmitted across C19 and C15 to the input at IC9 pin 4. This has the effect of synchronizing
the output of the pulse width modulator with the data sampling operations of the analog board
and keeps power supply switching spikes from interfering with those operations.
output at IC10 pin 2 goes High and with each successive press of the POWER
output at IC10 pin 2 is High, the MOSFET Q7 is turned on and pulls the gate of
Power Supplies
The secondary pins 7, 8, 9 of T1 form a center tap transformer, the voltage is rectified by D2
and D4 then filtered by C10, C11, C12 and C13. The resistor and capacitor combinations R66,
C113 and R68, C115 across the rectifying diodes D2 and D4 respectively are for EMI reduction.
The dual 12 volt supplies, +V12 and -V12 which are generated from this voltage are regulated
by IC7 and IC8 respectively. The secondary winding of pins 5 and 6 of T1 are rectified by D3
(R67 and C114 for EMI reduction) and filtered by C9, L1 and C20, this voltage designated as
VCC (+5 volts) acts as reference for IC9, supplies power for the opto isolator non-isolated side
and powers other circuitry on the board.
The secondary winding consisting of pins 2 and 3 are rectified and filtered by D1 and C1. The
rectified voltage at this point is approximately 7 volts DC and is regulated to 5 volts by IC2. This
isolated supply powers the isolated portion of the opto-isolators and the RS232 driver chip IC1.
The unregulated voltage VRAWI is sent to the rear panel connector J101.
Rev. 01 Model 2001 Service Manual 11
Section 4 Theory of Operation 2775 Main Board
The backup voltage (VBACK) is regulated by IC12 from the VIN supply. Capacitors C22 and
C27 serve as filters and D17 allows VCC to power VBACK circuitry when the monitor is on. At
this point D18 is biased off so IC12 is idle. When the monitor is turned off and VCC collapses
D18 is then forward biased and IC12 now supplies VBACK circuitry, D17 at this time is reverse
biased and prevents power from reaching VCC.
The saturation sensor LEDs derive their power (LEDSRC) from the current regulator IC32. (See
sheet 2 of 4 on schematic.) Resistor R31 limits the maximum steady state current draw to 45
mA (nominal draw 35 mA). Regulator output is filtered by C85 and L2. The charge stored on
capacitor C1 supplies the 290-350 mA peak currents that can occur when the sensor LEDs are
turned on. Diode D12 prevents the regulator output from exceeding +7.5 volts while the fuse,
F2, provides current limit protection in the event of a regulator circuitry failure. The RP 8 & 10
(pins 1,8 and 5,6) divider network provides the CPU (via IC33) with a means to monitor the
LEDSRC status.
The +VA and -V12 supplies are regulated to +V5 (+5 volts) and -V5 (-5 volts) by IC44 and IC43
respectively. These supplies are used by the 20 bit ADCs, the 8 bit ADC and other circuits
associated with them.
Voltage References
See sheet 2 of 4 on schematic.
A +2.5 volt precision reference supply (VREF), generated by IC35 from the +V12 supply, is
used as a reference voltage for the 20 bit ADC chips IC37 and IC34.
The +2.5 volt output from IC35 pin 6 is fed to the non-inverting input of amplifier IC36 pin 3.
Resistors R32 and R33 combine for a gain of 1.617 that provides a +4.096 volt reference
(approximately) supply, 4VREF, at IC31 pin 1. If jumper JP2 is shorted then VREF will be 3.0
volts and R32 will be adjusted so that 4VREF is still 4.096 volts.
The 4VREF is fed to IC30 pin 13 which is set up as a unity gain inverting buffer amplifier,
therefore the output at IC30 pin 14 is -4 volts. This -4 volts is used by IC29 as a reference
voltage for VLED (Voltage LED) and CNTRST (Contrast) controls. (See sheet 3 of 4 on
schematic.)
Preserving RAM and Real Time Clock Data
See sheet 4 of 4 on schematic.
The NAND gate output at IC11 pin11 will be Low when the monitor is on (IC10 pin 2 is High)
and High when the monitor is off (IC10 pin 2 is Low). This PWRON* (Power On) signal is used
to prevent corruption of RAM and real time clock data when the monitor is turned off. It does
this by going High and therefore denying CPU access to the RAM and real time clock so that
as the power supplies fall when the monitor is turned off, the CPU cannot send erroneous data
to these devices.
Whenever the CPU is writing information to the RAM or Real Time Clock, the CPU momentarily
sends the OFFDIS (Off Disable) line High. The High going level appears at IC11 pin 2. Since
the monitor is powered on, IC11 pin1 will be High. This means IC11 pin3 momentarily goes
Low, Q6 starts to conduct and IC10 pin 4 goes High. In this reset condition the Q1
flip-flop of IC10 (pin 2) will be held high even if the user presses the POWER key and clocks
the flip-flop. In effect, the CPU is not allowing the monitor to be turned off. The Low at IC11 pin3
will last for the duration of the RC time constant set by C21 and RP4 (pins 5,6). These values
were chosen to produce a time-out longer than the time necessary to complete the write to RAM
or Real Time Clock operation. After the RC time-out, IC10 pin 4 returns Low and a press of the
output #1
12 Model 2001 Service Manual Rev. 01
2775 Main Board Section 4 Theory of Operation
POWER key will toggle the Q1 output of IC10 and the monitor will turn off. This is done to
prevent corruption of RAM and Real Time Clock data.
Low Battery Voltage Shutdown
See sheet 4 of 4 on schematic.
The CPU monitors the battery voltage and provides the user with a low battery indicator,
messages and alarms. However, if these are ignored, a hardware circuit will take over and shut
off the monitor to prevent battery damage.
The pulse width modulator IC9 requires at least 7.6 volts at pin 7, its voltage supply, in order to
operate. This pin typically draws 10 mA of current. The resistance of the R63 and Q8
combination is approximately 114 ohms. This equates to a voltage drop of approximately 1.14
volts. Therefore if the battery voltage drops under 9.0 volts (approximately), IC9 will not have
sufficient voltage to operate and will shut down. Shutdown of IC9 stops current flow through
transformer T1 and the secondary supplies shut down, effectively turning off the monitor.
When IC9 shuts down, its VREF output at pin 8 is pulled Low. This forward biases D6 and
causes the NAND gate output at IC11 pin4 to go High. The #2 flip-flop of IC10 is clocked, and
the High at the D2 input (because Q1
at pin 13 Sets the #1 flip-flop causing the Q1
MOSFETs Q7 and Q8, thereby blocking any supply voltage from IC9 pin 7. Normally, pressing
the front panel POWER key would clock flip-flop #1 (at pin 3) and return the pin 2 output Highbut the High output at pin 13 keeps the #1 flip-flop Set-and the POWER key has no effect.
If at this point the AC MAINS is reconnected, MOSFET Q8 continues to block current from IC9
pin 7 and the monitor remains off. Connecting the AC Mains does however send the LINEST
signal High. This High Line Status signal is brought to IC10 pin10 where it Resets the #2 flipflop, sending IC10 pin 13 Low and removing the Set condition from flip-flop #1. Now, if the front
panel POWER key is pressed, flip-flop #1 is clocked, IC11 pin11 goes High, MOSFETs Q7 and
Q8 turn on, the supply to IC9 pin 7 is restored, the pulse width modulator restarts, energizes
T1, and the monitor turns back on.
is High) is transferred to the Q2 output at pin 13. The High
pin 2 output to go Low. This Low shuts off both
Timing Sequencer
See sheet 2 of 4 on schematic.
A 14 stage divider, IC39, acts as a timing sequencer. A 3.276 MHz crystal Y2, provides a Clock
(CLKSEQ) to IC39 pin 10. The RESET (IC39 pin 11) input resets IC39 on monitor power up.
The IC39 pin 9 Q1,output provides a clock input signal to the audio tone generator IC27. The
IC39 pin 3 Q14 output provides a 5 ms interrupt (INT5MS) for IC18. The Q4-Q11 outputs of
IC39 become inputs to the Data Sampling Controller IC42.
Data Sampling Controller
The IC39 Timing Sequencer’s Q4-Q11 outputs become inputs to IC42, a PEEL (Programmable
Electrically Erasable Logic) device. The PEEL uses the CLK and D0-D6 inputs, and the SC1
and SC2 inputs, to control data sampling by providing sensor LED drive signals and
demultiplexing for the signals returning from the saturation sensor.
The waveforms in Figure 1 (with the exception of CLK) are only valid when both the SC1 and
SC2 inputs are low. The System Calibration inputs (SC1 and SC2) generated by the
microprocessor, are kept low, except that they are toggled high/ low, during a Probe Off Patient
Rev. 01 Model 2001 Service Manual 13
Section 4 Theory of Operation 2775 Main Board
alert, and during a system power up self-test. See Calibrating the 20-Bit Analog-to-Digital
Converters on page 9.
Figure 1. Front-End Timing
The data sampling sequence consists of:
a. turn on the Red LED (RDLED*) and the Analog Sample line (ASAMP*)
b. allow the Red LED time to reach full brightness (steady state light output)
c. sample the Red LED return signal (RDSMP*)
d. turn off the Red LED, the Analog Sample line, and stop sampling
e. turn on the Infrared LED (IRLED*) and the Analog Sample line (ASAMP*)
f. allow the Infrared LED time to reach full brightness (steady state light output)
g. sample the Infrared LED return signal (ISMP*)
h. turn off the Infrared LED, the Analog Sample line, and stop sampling
i. repeat the process starting at step a.
The Analog Sample (ASAMP*) line is used to nullify the effects of any ambient light signals
returning from the sensor.
The IC42 INSIG* and SIGND* outputs are used in conjunction with the SC1 and SC2 inputs.
The IC42 pin 14 external sequencer (SYNC) line is equivalent to the PEEL’s D1 input. It
provides a “sync” pulse to the pulse width modulator on the power supply board in order to keep
power supply switching spikes from interfering with data sampling operations.
Sensor LED Drive Circuits
The VLED line voltage is derived from IC30 pin 8 which is controlled by the Digital to Analog
Converter IC29. (See sheet 3 of 4 on schematic.) When address line A0 is high (IC29 pin 6)
and both WR* (IC29 pin 16) and DACCS* (IC29 pin 15) are low the D/A Converter is enabled.
The data on lines D0-D7 (IC30 pins 14-7) now control the output voltage of IC30 pin 8 (VLED)
based on the VREFB voltage on IC29 pin 18.
See sheet 2 of 4 on schematic.
When the RDLED* signal at IC42 pin 18 goes low (logic 0), Q14 turns off and the Red LED
signal (VLED from IC30 pin 8) at R37 is divided by R37 and R41, finally causing IC36 pin8 to
go high. This positive output turns Q11 on and current flows from the LED source (LEDSRC),
through the Red LED in the sensor (it turns on) returning as LED1SK (LED1 sink) across Q11
and the current limiting resistor R53 to ground.
14 Model 2001 Service Manual Rev. 01
2775 Main Board Section 4 Theory of Operation
When RDLED* returns high (logic 1), Q14 is biased on, forcing IC36 pin 10 to ground potential:
Q11 is biased off, and as a result, the Red LED in the sensor is also off.
The Infrared LED drive circuit operates in the same manner as the Red LED drive discussed
above. The IRLED* signal at IC42 pin 17 activates Q13 the LED2S signal causes a positive
signal at IC36 pin 14, and current can flow from the LEDSRC supply through the sensor’s
Infrared LED, Q12, and the current limiting resistor R52 to ground.
Sensor Photodiode Return Path
See sheet 2 of 4 on schematic.
Light, from the sensor’s Red or Infrared LED, shines through the pulsating vascular bed (the
patient’s finger, toe, etc.) placed between the LEDs and the photodiode. Some of this light
emerges from the tissue and impinges on the photodiode, causing the photodiode to conduct
current. IC40 pins 1-3 is set up as a differential amplifier that converts this input current to a
voltage at the amplifier output. The sensors are wired such that photodiode current produces a
positive voltage at IC40 pin 1.
The voltage at IC40 pin 1 is presented to an analog switch IC41 pin 6. This switch is controlled
at pin8 by INSIG* (Input Signal) from IC42, and will be closed (IC41 pins 6 and 7 connected)
except if the monitor is in a Probe Off Patient condition or is undergoing its Self-Test at system
power up. The switch IC41 pins 9-11, controlled from SIGND* (Signal Ground) at IC42 will be
open (no connection between IC41 pins10 and 11) except as noted above for the switch at IC41
pins 6-8. As a result, the IC40 pin 1 voltage passes undisturbed to the high pass filter consisting
of R59 and C90.
As shown in Figure 1., the ASAMP* signal is active whenever either sensor LED is turned on.
This causes Q15 to turn off and the charge at C90 passes through the unity gain buffer to IC40
pin 5.
If the signal at IC40 pin 7 is the product of the Red LED being turned on, then RDSMP* from
IC42 pin 12 will go low and close the switch at IC41 pins 2-3, thereby presenting the signal to
a sample and hold circuit consisting of R54 and C100 (that maintains the signal until next
sample pulse arrives), a gain stage (IC38 pin 1), a filter/divider network (C87, R45 and R46),
and finally, to the Red channel Analog-to-Digital Converter (ADC) IC34.
If the signal at IC40 pin 7 is the product of the Infrared LED being turned on, then ISMP* from
IC42 pin 13 will go low and close the switch at IC41 pins 14-15, thereby presenting the signal
to a sample and hold circuit consisting of R55 and C96 (that maintains the signal until next
sample pulse arrives), a gain stage (IC38 pin 7), a filter/divider network (C88, R49 and R50),
and finally, to the Infrared channel Analog-to-Digital Converter IC37.
Again referencing Figure 1., the ASAMP* line returns to a logic high when neither LED is being
driven, causing Q15 to turn on. With Q15 conducting, any charge at C90 is discharged to
ground and the next pulse will charge C90 from a known level. If it were not for Q15, any charge
remaining on C90 from the previous pulse or from ambient light reaching the photodiode would
be added to the charge from a new pulse-creating measurement errors.
Calibrating the 20-Bit Analog-to-Digital Converters
See sheet 2 of 4 on schematic.
The 20-bit ADCs are calibrated as part of the system self-test which occurs each time the
monitor is turned on. At power up, the microprocessor sets the CAL line high. The System
Calibration input SC1 is set high and SC2 is reset to a logic low. The CS5503 ADC will not
Rev. 01 Model 2001 Service Manual 15
Section 4 Theory of Operation 2775 Main Board
operate while the CAL line is high. On the falling edge of the CAL signal, the ADC will initiate a
calibration cycle determined by the state of the SC1 and SC2 inputs.
The high at SC1 and the low at SC2 cause the Data Sampling Controller, IC42, to set INSIG*
high and reset SIGND* to a logic low. The high INSIG* opens the switch at IC41 pin8 so that
IC41 pins 6 and 7 are no longer connected- disconnecting the returning photodiode signal from
the rest of the circuitry. The low SIGND* signal closes the switch at IC41 pin 9 and as a result,
the input to the C90-R59 high pass filter (and thus the entire ADC input circuitry) is brought to
ground potential.
The CAL line (which went high at power up) is reset low and ADCs IC34 and IC37 begin their
calibration cycles. Because the analog input circuitry is grounded via SIGND*, only circuit offset
voltages can be present at the AIN (pin 9) input. The calibration cycle sets the ADC “zero” point
to equal this voltage, thus compensating for any circuitry offsets. The ADC then sets its “full
scale” point to equal the voltage at its VREF (pin 10) input. This completes the calibration cycle.
The ADC can now start sampling its input and converting it to a 20-bit digital word. The
processor resets SC1 to a logic low, causing IC41 pin 9 to open and IC41 pin 8 to close. The
photodiode signal can now reach the ADCs.
20-Bit Analog-to-Digital Conversion
See sheet 2 of 4 on schematic.
Data from the Red and Infrared channels is sampled by the 20-bit measurement ADCs, IC34
and IC37 respectively. The analog input at pin 9 is converted to a digital representation with 20bit resolution based on the input magnitude.
The CS5503 A/D converter continuously samples its input, converts the value to a digital word,
puts the word in its output buffer (overwriting previous buffer contents), then repeats the
process by again sampling its input. The frequency of the sample/convert/overwrite-buffer
sequence is based on the 3.2768 MHz clock signal at the ADC pin 3 (CLKSEQ) input.
The microprocessor starts a read cycle of the Infrared channel by bringing IC37 pin 16 (Chip
Select Channel 1) low. A Red channel read starts when IC34 pin 16 (Chip Select Channel 2) is
brought low.
On the falling edge of the ADC’s CS*, the output word’s MSB (most significant bit) appears at
the pin-20 SDATA (Serial Data) output. The SDATA line connects directly to the
microprocessor’s serial input (RXS) pin. The remaining bits (in descending order) are output
from SDATA with subsequent falling edges of the Serial Clock (SCLK) input at pin 19. The
SDATA output automatically goes to a 3-state (high impedance) condition after completing a
word transmission, thus freeing the data line for other uses (i.e., the other ADC channel).
The Serial Clock speed is controlled through the digital board PEEL IC18. This clock rate is
significantly slower than the ADC sampling rate. As a result, the ADC rewrites its output buffer
with new information at a faster rate than the data can be read from the buffer. No conflict
occurs, however, because while CS* is low (during the read cycle), the ADC does not update
its output buffer (the current word is not overwritten). After the processor receives the entire
word, it allows the converter’s CS* to return high, and the ADC resumes its sample/convert/
overwrite-buffer cycle.
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2775 Main Board Section 4 Theory of Operation
Sensor Status Decoding and Conversion
The microprocessor monitors several sensor parameters in addition to the Red and Infrared
data channels. It monitors the status parameters, as well as the voltage of the monitor’s internal
battery.
The 8-to-1 multiplexer, IC33, decodes the A0AUX-A2AUX input address lines and connects
one of eight status parameter inputs (labeled channels 0-7 at IC33) to the multiplexer output at
IC33 pin 3. Resistor R29 and diode D13 prevent negative voltages from reaching the input to
the analog-to-digital converter, IC31.
IC31 is an 8-bit analog-to-digital converter with a serial data output. While the IC31 Chip Select
(CS) input is high, the CLK input and DOUT output are in 3-state mode. When CS is brought
low (under processor control), the most significant bit (D7) of the PREVIOUS data conversion
becomes available at the DOUT pin. The remaining bits (D6-D0) are shifted out on subsequent
falling edges of the CLK input. On the clock pulse following the one that shifts out the least
significant bit (D0), the CLK and DOUT lines are returned to 3-state and the ADC performs a
new conversion based on the input it receives from the IC33 channel selected by the A0AUXA2AUX input address lines.
The ADC sample/convert/store-result cycle is based on internal chip timing and not the CLK
input which (along with CS) only controls serial data output. Thus the CS line is free to return
high once the ADC cycle begins.
Sensor Status Parameters
The sensor (and battery) status parameters input to the multiplexer IC33 are described below.
Note that channel number refers not to the IC33 pin number, but to the signal label (e.g.,
channel I0 signal resides at IC33 pin 13).
Channel I0: ADCV12.
This is an extra input to the multiplexer IC33 pin 13. It is unused as of this writing.
Channel I1: Auxiliary Input.
This is an extra input to the multiplexer IC33 pin 14. It is unused as of this writing.
Channel I2: Photodiode DC Level.
Resistors R40, RP8 (pins 1, 2) and capacitor C97 form a voltage divider and low pass filter that
provide a measure of the mean DC level at the output of the photodiode current-to-voltage
amplifier IC40 pin 1. This channel (IC33 pin 15) is used in determining ambient light
interference. If this line is examined while the sensor’s Red and Infrared LEDs are turned off,
then any DC level at IC40 pin 1 must be the result of ambient light impinging on the photodiode.
If the DC shift is in excess of limits set in the software, a Light Interference message appears
on the monitor’s display.
Channel I3: Sensor LED Supply Voltage.
This channel, at IC33 pin 12, monitors the sensor LED supply voltage through a voltage divider
consisting of RP10 (pins 5, 6) and RP8 (pins 1, 8). If a fault occurs that causes the LED supply
fuse F2 to blow, or if the sensor wires are shorted, this channel reports the condition and the
Message Center displays FAULTY SENSOR.
Channel I4: Incompatible Probe Detection
The input at IC33 pin 1 provides the processor with an incompatible probe indicator (the words
probe and sensor are interchangeable). The photodiode output voltage at IC40 pin 1 will be
positive if a SuperBright™ series sensor is connected to the monitor. This positive signal
passes through the high pass filter of C73 and RP10 (pins 7, 8) to the amplifier inverting input
Rev. 01 Model 2001 Service Manual 17
Section 4 Theory of Operation 2775 Main Board
IC36 pin 6, where it is summed with the -5 volt output from IC43. The resultant voltage at IC33
pin 1 will be approximately +2.81 volts with no photodiode input. This voltage drops as the
(positive) photodiode signal at IC40 pin 1 increases. If the IC40 pin 1 signal goes negative, as
would happen if a non-SuperBright™ 8600 series sensor were connected to the monitor, the
cumulative effect of the -5 volts and the negative photodiode signal passing through D14 and
R34 would be to send the IC36 pin7 output to its positive rail (+12 volts). The processor
recognizes this higher voltage and causes a fault or error message to be displayed.
Channel I5: Infrared LED Cathode Voltage.
A low pass filter consisting of RP10 (pins 3, 4), RP8 (pins 1, 7) and C89 provides a means to
measure the cathode voltage of the sensor’s Infrared LED. If the channel at IC33 pin 5 is
sampled the monitor can determine if the LED is open circuit (zero volts at IC33 pin 5) or
operational (approximately 2.5 volts at IC33 pin 5). If not operational, a fault or error message
is generated.
Channel I6: Battery Supply Voltage
The monitor’s internal battery voltage is divided down by RP3 (pins 7, 8) and RP8 (pins 1, 5).
The voltage at IC33 pin 2 is monitored and if its magnitude is less than a predetermined value
(encoded in the software) the monitor lights and/or flashes its front panel battery indicator. This
provides the user with a low battery warning.
Channel I7: Red LED Cathode Voltage.
A low pass filter consisting of RP10 (pins 1, 2), RP8 (pins 1, 6), and C92 provides a means to
measure the cathode voltage of the sensor’s Red LED. If the channel at IC33 pin 4 is sampled
the monitor can determine if the LED is open circuit (zero volts at IC33 pin 4) or operational
(approximately 2.5 volts at IC33 pin 4). If not operational, display message ERROR - FAULTY
SENSOR is generated.
Microprocessor
See sheet 1 of 4 on schematic.
A Hitachi HD64180RP microprocessor directs the actions of the Model 2001 Pulse Oximeter.
The processor, IC16, is operated at 6.144 MHz (half the12.288 MHz frequency of crystal Y1),
has an 8-bit data bus and a 19-bit address bus (the 2001 uses only 18-bits). The
microprocessor also provides two asynchronous serial communication channels, a clocked
serial I/O port and various interrupt and control signals. The +5 volt VCC supply to the
processor is first sent through inductor FB1, a ferrite bead, before powering the chip at IC16 pin
32.
Memory
See sheet 1 of 4 on schematic.
The Model 2001 system software is located at IC17, a 29C010 Flash EPROM. The 32 K byte
RAM, IC20, stores trend data, system power up settings (averaging times, serial output
parameters, etc.), and provides an area for system (scratch pad) memory requirements. Since
IC20 is powered from the VBACK supply, RAM memory is retained when the monitor is turned
off and it becomes available again when the monitor is turned back on.
The ROM at IC17 is read when its Chip Enable line (IC17 pin 22) is brought low by the ROMCS*
signal at IC25 pin 3, and the processor brings its Read line (IC16 pin 63) low-thereby activating
the ROM Output Enable line at IC17 pin 24. Under these conditions, ROM data from the
specified address bus location is made available to the data bus for use by the processor.
18 Model 2001 Service Manual Rev. 01
2775 Main Board Section 4 Theory of Operation
The RAM (IC20) is activated when its Chip Select line RAMCS* (IC20 pin 20) is brought low,
via IC25 pin 8. When the ME* line at IC25 pin 5 is low, and the inverse of address line A17 at
IC25 pin 4 is low, output pin 6 of IC25 will go low. This in turn will drive IC25 pin 10 low, with
PWRON* low at IC25 pin 9, IC25 pin 8 will be low (RAMCS*). If at that time, OE (IC20 pin 22)
is low, a RAM Read occurs, whereas a RAM Write will occur if WE
(IC20 pin 27) is low.
Real Time Clock (RTC)
See sheet 3 of 4 on schematic.
A Real Time Clock (IC24) provides the Model 2001 the ability to time stamp collected (printed)
trend data. The 32.768 kHz crystal, Y3, provides the timing signals for the clock chip, which is
powered from the VBACK supply so that the clock can continue to keep time when the monitor
is turned off (provided the monitor’s 12 volt internal battery is connected and maintains at least
a nominal charge).
The RTC is activated when its Chip Select line (CS0
monitor on PWRON* will be low (IC25 pin 13), the RTC* line will be brought low by the
processor through IC22 pin 14 (see sheet 1 on schematic), these lines drive RTCCS* (Real
Time Clock Chip Select IC25 pin 11) low. If at this time, the RD* (IC24 pin 8) input is low, a RTC
Read occurs, whereas a RTC Write will occur if the WR
is handled by A0-A3 (pins 4-7) and data I/O through D0-D3 (pins 14-11).
) at IC24 pin 2 is brought low. With the
(IC24 pin 10) input is low. Addressing
Sound generator
See sheet 3 of 4 on schematic.
A programmable tone generator, IC27, is used to drive the monitor’s audio circuit. The tone
generator is clocked by IC39 pin9 from the 1.638 MHz signal, Q1. The tone generator is
enabled by the processor when IC22 pin12 is brought low. While CE
and data bus information including frequency (pitch) and attenuation (volume) is accepted by
the tone generator. The Ready signal (IC27 pin 4) goes low while accepting data and the
processor is put into a Wait state until IC27 finishes its task; then Ready returns high and the
processor continues its operations.
The AUDOUT output at IC27 pin 7 drives the audio amplifier IC26. The amplifier output is
coupled through capacitors C55 and brought to J109 as the SNDOUT (Sound Out) line. The
speaker which is mounted in the chassis is connected to J109, LS1 is not installed on the 2775
Main Board.
is low, WR is brought low
Keypanel Interface
See sheet 3 of 4 on schematic.
The 10 keys (switches) on the Model 2001 front panel are connected to the 2775 Main Board
through a ribbon cable at J104. Each key (except POWER) is connected to an 8-bit latch (either
IC14 or IC15). When any of these keys is pressed, the corresponding latch input is brought low.
The processor continually reads the status of these latch outputs, the RDKEY* enables IC14
when low and the RDKEY_2* line enables IC15 when brought low.
The POWER key ON/OFF signal is sent through J104 pin 15. The AC Line Status signal,
LINEST, is generated by the power supply, and is high (+5 volts) when the monitor is connected
to the AC Line (Mains) and the rear panel switch is set to “|”. This +5 volt level is sent to LED
D2 (the green indicator) on the keypanel via J104 pin 16. The LINEST signal is also input to the
Rev. 01 Model 2001 Service Manual 19
Section 4 Theory of Operation 2775 Main Board
latch at IC14 pin 8 so that the CPU can detect if the unit is operating on AC line power (IC14
pin 8 high) or on battery power (IC14 pin 8 low). Diode D9 keeps current from back feeding into
IC14 when the monitor is turned off but still connected to the AC line.
The 2MIN (D3), AUDIO OFF (D4), ALERT (D5), and LOW BAT (D1) LEDs are driven by the 8bit latch IC13. When each of the corresponding signals is driven high the appropriate LED on
the keypanel is illuminated.
Display Interface
See sheet 1 of 4 on schematic.
The display is connected to the 2775 Main Board at J107. It is controlled by the processor using
the RD* (Read), WR* (Write), and DISPCS* (Display Chip Select) lines. Data bits D0-D7 are
used as input/output lines and A0 is used in conjunction with the RD* and WR* lines to
distinguish between read and write operations as listed below.
A0 RD* (active low) WR* (active low)
High Status Read Command Write
Low Data Read Data Write
Table 1. Display Command/Data table.
See sheet 3 of 4 on schematic.
The CNTRST (Contrast) line is controlled by pressing the front panel key. When depressed and
held the processor controls the digital to analog converter IC29, line A0 is brought low along
with WR* and DACCS*, the data on D0-D7 controls the voltage at IC30 pin 7 which can vary
from 0-4 volts. The output of IC30 pin 7, along with 4VREF feeds a summing amplifier (IC30
pins 1, 2, 3). The output of the summing amplifier IC30 pin 3 controls the base of Q10 which in
turn controls the contrast of the display through a variable negative voltage.
The backlight for the display is controlled by the DSPBR (Display Bright) line. When DSPBR is
high the gate of Q16 is biased off, current flows from Vcc through R51 to IC45. This sets the
backlight for low illumination. The illumination of the backlight is made greater when DSPBR is
made low, this biases Q16 on which essentially shorts out R51 allowing more current to flow
into IC45 increasing the intensity of the backlight.
I/O Device Controller
See sheet 1 of 4 on schematic.
The A/D Converter Chip Selects, serial A/D Chip Selects, Sensor Status Decoding and NEXT*
line are all controlled by IC28 when selected by the OPORT line (IC21 pin 10). The OPORT line
will go high when the L1* and WR* line both go low at IC23 pins 13 and 12, this will send output
pin IC23 pin 11 low which drives inverter IC21 pin 10 high enabling IC28.
A 3 to 8 decoder is used to control the DACCS*, RTC*, DISPC*, AUD*, KEY*, L1*, L2*, 2KEYS*
lines. when the IOE* line goes low and the LIR* line goes high being inverted by IC21 pin 2 and
presented to IC22 pin 5 as a low enable line IC22 is enabled, Q0-Q7 will be driven low
depending upon the A4, A5 and A6 lines on pins 1, 2, 3 respectively on IC22.
With the LPORT line high IC13 is enabled, this latches the data on lines D0-D7 (1D-8D pins 2-
9) on its output pins 19-12 (1Q-8Q respectively), the outputs correspond to the following eight
lines:
CAL-used by the A/D Converters on power up to compensate for front end voltage offsets.
20 Model 2001 Service Manual Rev. 01
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