I-O Display Systems Basic I-O Product User Manual

Basic I/O Product Family

NOTICE:

This document contains two separate users manuals.

The first section should be used for the BIO4, BIO8, and BIO16 products.

The second section should be used for the BIO4AD, BIO8AD, and the BIO16AD
products.

If you find that you have any questions with the setup or installation of any duTec
product please feel free to call us:

Phone: [phone]
or
E-mail: [e-mail]

Vol.1 Table of Contents

The Basic I/O ........................................................... 1 - 1

ANALOG INPUTS .............................................. 1 - 2

DIGITAL INPUTS............................................... 1 - 4

DIGITAL OUTPUTS: ............................................ 1 - 5

SYSTEM THROUGHPUT ........................................ 1 - 6

COMMUNICATION PROTOCOL .................................. 1 - 8

Available I/O Modules ............................................ 1 - 9

DIAGNOSTICS ................................................ 1 - 10

PHYSICAL CHARACTERISTICS ................................. 1 - 10

PRODUCT TEST ............................................... 1 - 11

Warranty: ..................................................... 1 - 11

MOUNTING ........................................................... 2 - 1

POWER WIRING ....................................................... 2 - 2

COMMUNICATING WITH THE BASIC I/O ................................. 2 - 3

Multidrop ...................................................... 2 - 4

Repeat......................................................... 2 - 4

RS-422 ........................................................ 2 - 5

RS-485 ........................................................ 2 - 5

RS-485 Programming ............................................. 2 - 6

COMMUNICATION WIRING ............................................. 2 - 7

Network load V.S. Noise suppression ........................................ 2 - 8

Network Bias Resistors ........................................... 2 - 8

RS-422 HOST TO BASIC I/O ...................................... 2 - 9

BASIC I/O TO BASIC I/O RS-422 ................................. 2 - 10

RS-485 Host to BASIC I/O ....................................... 2 - 11

BASIC I/O to BASIC I/O RS-485 (Multidrop only) .................... 2 - 12

BASIC I/O Setup ....................................................... 2 - 13

Analog/ Digital ................................................. 2 - 14

Addresses ..................................................... 2 - 14

Baud Rates .................................................... 2 - 14

Protocol Handshake Types ........................................ 2 - 15

Network Type Switch ............................................ 2 - 16

-i-

Vol. 1 Table of Contents

Communication verification............................................... 2 - 18

Hardware error codes .................................................... 2 - 19

Hardware watchdog ..................................................... 2 - 19

Sensor/ Actuator I/O wiring ............................................... 2 - 19

Analog Inputs: ................................................. 2 - 20

Analog Outputs: ................................................ 2 - 22

Digital Inputs: .................................................. 2 - 23

Digital Output Wiring............................................ 2 - 24

-ii-

The Basic I/O 1

THE BASIC I/O:

BASIC I/Os are a family of small, industrial grade, remote data acquisition and control
systems which exchange data with a Host computer via a serial communications link.
Controlled by a wide range of software running on a Host computer, Basic I/Os are located
near the sensors and actuators. The serial link eliminates the need for expensive and noise
prone signal wiring between field sensors and actuators, and a central control room.

Each BASIC I/O system consists of one logic board connected to a 4, 8, or 16 position I/O
module mounting rack. This combination is then field configurable to accept either analog or
digital electrically isolated input or output modules which can interface to a wide variety of
sensors and actuators.

BASIC I/O networks can service over 4000 analog and/or digital I/O lines in various
combinations.

User selected serial communications between the Host and the first BASIC I/O can be RS­422 or RS-485. These communications links allow the units to operate up to 5000 feet apart.
Baud rates from 300 to 38,400 are available.

The BASIC I/O instruction set core complies 100% with that of the OPTO- 22 Optomux ™
With this ASCII character, speak-only-when-spoken-to protocol, a Host transmits inquiry
requests to the BASIC I/O to determine the status of its various process inputs. Similarly, the
software in the Host computer makes control decisions and transmits instructions to the
BASIC I/O, which in turn, makes the proper changes to its various outputs. Both the Host and
its communications link are essential elements in this data acquisition and process control
scheme.

Software for use with the BASIC I/O system can be obtained from a variety of sources.
Nearly every third party SCADA software vendor has developed a driver which is compatible
with this system. In addition, the communication protocol employed by the BASIC I/O
product is a published ASCII printable standard. This makes developing your own software a
simple matter. duTec also offers a software solution called EASY I/O. With this package,
custom QuickBASIC source code is generated to fit the signals generated to fit the signals
located on the BASIC I/O. Once configured, a simple data acquisition program is
automatically generated. This sample can then be altered to fit the particular needs of the user.

1-1(Vol.1)

.

The Basic I/O 1

A notable feature of the BASIC I/O is its ability to gather data and perform ranging and
statistical operations on raw data before it is sent to the Host. The Host can thus spend less
time manipulating data and more time gathering it. The following sections discuss the
different signals the BASIC I/O can handle.

ANALOG INPUTS:

duTec analog input modules are 100% isolated and accept a wide range of voltages, currents,
the outputs of thermocouples, RTDs, and 590 type temperature probes.

BASIC I/O instructions provide linearized thermocouple and RTD sensor data. Engineering
unit conversion is performed by the host software, such as duTec’s EASYIO program
generator.

The BASIC I/O samples individual analog inputs at the constant rate of samples per second.
The effective sample rate per channel is determined by the total number of channels to be
sampled.

Analog input instruction types are:

Input Value Determines signal levels, with 12 bit (1 part in 4096) resolution

Offsets Input values can be software offset or “Zeroed” with 12 bit (1 part in

4096) resolution over the module’s specified range.

Gain/Slope The amplitude of input values can be software multiplied by factors

ranging from 0.25 to 4.0.

Range Limits The occurrence of input values falling out of user defined upper or

lower limits can be flagged.

Minimums The minimum level of input values can be captured.

Maximum The maximum level of input values can be captured.

Averages Can calculate average input amplitude for 1-65,535 samples.

Temperature Provides linear temperature in C for thermocouples, RTD and type

590 temperature probes.

Thermocouple modules provide cold reference junction compensation.

1-2(Vol.1)

The Basic I/O 1

ANALOG OUTPUTS:

Analog output modules are 100% isolated. These self-sourcing modules provide the voltage or
current necessary to drive standard instrumentation loads. All are updated every 10 Ms, or 100
times per second.

Analog output instruction types are:

Level Value Can set output levels, as a fraction of the module’s full scale

range, and are specified with 12 bit (1 part in 4096) resolution.

Waveforms Can provide square, triangle, sawtooth or ramp waveforms,

Maximum and Minimum amplitudes, as a fraction of the output
module’s full scale range, are specified with 12 bit (1 part in

4096) resolution. Waveform periods are specified from 0.1 to
6,553 seconds (about 109 minutes).

1-3(Vol.1)

The Basic I/O 1

DIGITAL INPUTS:

Digital input modules detect the presence or absence of a field signal. Module types vary from
AC to dry contact sense. Because the industry standard modules are optically isolated, the
response time performance of digital input instructions can be limited by the delay in the input
modules themselves. Some modules can have rise and fall times of up to 40 milliseconds.

Digital input instruction types are:

Read Read the On or Off state of all inputs. This data is

updated every 10 Milliseconds.

Edge Detection Off-to- On and On-to-Off transitions can be detected

within 1 millisecond of their occurrence. Action is
only reported every 10 milliseconds.

Pulse Widths BASIC I/Os can report pulse width measurements

from .01 seconds to 46.6 hours. Minimum resolution
is .01 seconds (Pulse widths up to 10.9 minutes).
Either on or off pulses can be measured.

Pulse Counting Pulses can be counted up to a total of 65,535. To be

reliably counted, pulses must have a minimum On and
Off time of 1 millisecond. Thus the maximum
counting rate for a 50% duty cycle square wave is
once every 2 milliseconds (500Hz).

Frequency Direct frequency measurements can be made on

digital inputs at rates of up to 500 Hz with a user
specified time base of from .01 to 2.55 seconds.

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The Basic I/O 1

DIGITAL OUTPUTS:

Digital output modules, commonly referred to as solid state relays, control external AC or DC
power sources. A dry-contact (mechanical relay) with very low contact resistance is also
available.

Digital output instruction types are:

Set outputs Can set individual or multiple outputs On or Off.

Pulse Generator Can generate 1 to 65,535, 50% duty cycle pulses whose equal

On and Off periods can range from 0.01 to 2.55 seconds.
Resolution can be reduced by a factor of 1-256 on a system
wide basis to increase the maximum pulse width available.

Modifiers:
One Shot Can generate On or Off pulse durations of up to 10.9 minutes

Delayed Can generate delayed On or Off outputs after delaying up to

Square wave Can generate square waves with programmable On and Off

with a resolution of 0.01 seconds. Resolution can be reduced by
a factor of 1-256 on a system wide basis increasing duration up
to 46 hours. Re-triggering is available.

10.9 minutes with a resolution of 0.01 seconds. Resolution can
be reduced by a factor of up 1-256 on a system wide basis
increasing the delay before changing state up to 46.6 hours. Re­triggering is available.

periods. On and Off periods have a base range from 0.01
seconds to 10.9 minutes. Resolution can be reduced by a factor
of 1-256 on a system wide basis increasing duration to 46.6

hours

.

1-5(Vol.1)

The Basic I/O 1

SYSTEM THROUGHPUT:

Input data throughput is the time from beginning of the first character of an input instruction
to the end of the last character of the response. The processing time of the Host computer will
affect the effective throughput.
Output Execution throughput is the time from the beginning of the first character of an
instruction until the actual output changes. Because the instruction acknowledgment occurs
before the outputs actually change state, the processing time of the host computer controlling
output instructions can reduce the effective throughput. This is even possible at 38,400 baud
to instruct the BASIC I/O to turn a digital output on and then immediately instruct it to turn

back off so quickly that the module never actually gets activated
Tables below show milliseconds per channel and channels per second for 1 and 16 I/O

channel cases

Baud Rate mSec/

300 501 2 501 32 379 3 379 42

600 251 4 251 64 195 5 195 82

1200 126 8 126 127 104 10 104 154

2400 64 16 64 252 58 17 58 277

4800 32 31 32 496 35 29 35 458

9600 17 60 17 962 23 43 23 682

19200 9 113 9 1816 18 56 18 902
38400 5 204 5 3261 15 67 15 1076

Baud Rate mSec/

300 639 2 2639 6 484 1984 2 8

600 323 3 1323 12 250 4 1000 16

1200 164 6 664 24 134 7 509 31

2400 85 12 335 48 75 13 263 61

4800 46 22 71 94 46 22 140 114

9600 26 39 88 181 32 32 78 204

19200 16 63 47 339 24 41 48 335

38400 11 91 27 602 21 48 32 494

.

1 Channel 16 Channels 1 Channel 16 Channels

Input (Digital M) Output (Digital J)

Chan/Sec mSec/

Chan

Input (Analog L) Output (Analog S)

1 Channel 16 Channels 1 Channel 16 Channels

Chan/

Chan

Sec

THROUGHPUT TABLES

Chan/ Sec mSec/

16 Ch

mSec/

Chan/ Sec mSec/

16 Ch

Chan

Chan

.

Chan

/Sec

Chan

/Sec

mSec/
16 Ch

mSec/
16 Ch

Chan /Sec

Chan /Sec

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The Basic I/O 1

It should be noted that the values in the preceding throughput tables and the following
equations reflect only the communications overhead and inherent processing delay of the
BASIC I/O equipment. In practice, a significant amount of overhead will be devoted to other
processing tasks such as screen updates, Data logging, etc... Typically these other tasks
become the limiting factor in the “overall” throughput.
The equations below can be used for determining the hardware’s role in throughput for any
number of channels. (t is in Milliseconds) Throughput for digital I/O is independent of the
number of channels.

Digital Input Data

t digital Input = 1000*((150/Baud Rate) +0.001)

Digital Output Execution

Throughput for analog I/O varies with the number of channels, n.

Analog Input Data

Analog Output Execution

For determining the throughput for systems with a mixture of analog and digital data inputs
and the execution of analog and digital outputs, it is necessary to determine the time for each
instruction using these equations. The sum of these, t, In milliseconds, is the time required to
provide the service required by all instructions.

Dividing this sum into 1000 (milliseconds) yields the number of cycles per second.

(Digital M) Time for 1-16 channels:

(Digital J) Time for 1-16 channels:

t digital Output = 1000 ((110/Baud Rate) +0.012)

(Analog L) Time for n channels:

t analog Input = 1000 *(((150 + 40 * n)/Baud Rate) + 0.006)

(Analog S) Time for n channels:

t analog output = 1000 *(((110 + 30 *n)/Baud Rate) + 0.017)

t=t digital Input + t digital Output + t analog Input + t analog Output

Complete cycles/ Sec = 1000/ t

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The Basic I/O 1

COMMUNICATION PROTOCOL:

The BASIC I/O Communication Protocol is 100% compatible with the Opto-22 Optomux™
protocol. This ASCII printable serial protocol uses a “speak-only-when-spoken-to” format
where only the host can initiate an information exchange. Each BASIC I/O unit installed in a
network has a unique address. This address is embedded in the instruction generated by the
host computer. Every BASIC I/O chassis receives the instruction but only the unit which is
set to the address found in that instruction will respond. Every string of data whose length is
greater than one character is followed by a checksum to ensure data integrity. This protocol
also provides an instruction verification mode for further data transmission reliability.

As a result of the specific nature of the BASIC I/O communications protocol, the RS-422 or
RS-485 network can be shared with other devices whose protocol is similar.

A knowledge of serial communications, hexadecimal to decimal conversion, and string data
manipulation is required to compose custom user generated Host software. DuTec’s EASY
I/O software is designed to minimize these obstacles.

1-8(Vol.1)

The Basic I/O 1

ANALOG INPUTS, 12 BIT ANALOG OUTPUTS, 12 BIT

IIF10K-B Input 300Hz -10KHz OV1 Output 0-1V, self-sourcing

Frequency

IF2.5K-L Input 0-2.5KHz OV5 Output 0-5V, self-sourcing
IF5K-l Input 0-5KHz OV10 Output 0-10V, self-sourcing

IF10K-L Input 0-10KHz

IV25M Input 0-25mV OI420 Output 4-20mA, self-sourcing To 275 Ohm

IV50M Input 0-50mV
IV100M Input 0-100mV
IV1 Input 0-1V
IV5 Input 0-5V AC
IV5B Input Bipolar +/-5V IAC5 Input 90-140Vac
IV10 Input 0-10V IAC5A Input 180-280Vac
IV10B Input Bipolar +/-10V DC

IVAC Input 28-140Vac IDC5D Input 3-32Vdc Fast, >500Hz
IVAC-A Input 56-280Vac IDC5S* Input Dry Contact Sense Built-in Isolated

II420 Input 4-20mAdc
IIAC5 Input 0-5Aac

ITCE Type E 0 To 435 C AC
ITCJ Type J 0 To 700 C OAC5 Output 12-140Vac, 3.5A
ITCJ-1 Type J -80 To 750 C OAC5A Output 24-280Vac, N.C.(Normally Closed)
ITCK Type K -100 To 924 C OAC5J Output 20-280Vac, 6.0A
ITCK-1 Type K -110 To 1250 C
ITCR Type R 0 To 960 C DC
ITCR-1 Type R 0 To 1760 C ODC5 Output 5-60Vdc, 3.5A
ITCS Type S 0 To 1034 C ODC5A Output 4-200Vdc, 1.0A
ITCS-1 Type S 0 To 1760 C ODC5R Electro-Mechanical 0.5A Relay Form A,

ITCT Type T -200 To 224 C
I TCT-1 Type T -120 To 400 C
ITCT-2 Type T 0 To 150 C IDC5Z* Input +/-200mV, 0-10KHz Digital**

ITR10 10 Ohm Cu -55 To 150 C
ITR100 100 Ohm Pt -55 To 350 C
ITR100-1 100 Ohm Pt 0 To 100 C Fuses

ITP590 -188.4 To 150 C FM-1 Fuse assembly, 1.0A
ITP590-1 -50.0 To 150 C FM-3 Fuse assembly , 3.0A

Voltage

Voltage

Current

Thermocouple

RTD

Type 590 Temperature Sensor FM-06 Fuse Assembly 0.062A

Available I/O Modules

Current

load.

DIGITAL INPUTS

Voltage Source

IDC5NP Input 10-32 Vdc, 15-32Vac Non-Polarized

DIGITAL OUTPUTS

Normally Open (NO)

SPECIAL PURPOSE

SPS-1* Sensor Power Supply 18-24 Vdc, 30mA
TI01 Digital Input/ Output Test Module with Field

Switch and LED

SUPPORT PRODUCTS

FM-5 Fuse assembly, 5.0A

* When selecting a power supply for the system assume 25mA for standard digital modules and 100 mA
for marked with an *** The IDC5Z module is used for low-level signals and will pass signals at the rate
of 10KHz The BASIC I/O however, is limited to signals up to 500Hz.

1-9(Vol.1)

The Basic I/O 1

DIAGNOSTICS:

To confirm internal operations and communications link integrity, a set of built-in diagnostics
test key system functions each time power is applied. Diagnostics reduce both installation
debugging and operation troubleshooting.
A hardware watchdog timer insures safe shutdown in the event of processor or software
failures by turning all outputs OFF. Normally ON modules are available for those loads that
must remain ON.

PHYSICAL CHARACTERISTICS

Power Requirements

Voltage: 5.0-5.4Vdc
Current: 250mA +25mA Per digital module.
Note that the current draw of some specialized digital modules Such as the IDC5S or the

ODC5R, can be substantially larger Than 25mA. Consult the specific module data sheet for
this Value when sizing power supplies.

Operating Temp. 0 C to 60 C Contact factory for other operating temp

Ranges
Humidity 95% non-condensing
Weight 22 oz. Max (BIO16) Not including modules.

BASIC I/Os are ready to install, only dc power, communication and sensor or actuator wiring
is required

1-10(Vol.1)

The Basic I/O 1

PRODUCT TEST

Every BASIC I/O is burned-in at 70 °C while operating in a network for a period of 24 hours
prior to shipment.

Every analog I/O module is operated and tested while it’s ambient operating temperature is
cycled over the specified operating range of 0°C to 60°C for a period of 24 hours.

BASIC I/O Models:

BIO4 4 Position BASIC I/O Unit Includes SLB Logic Board and SMB4 Module board

less modules and power supply.

BIO8 8 Position BASIC I/O Unit Includes SLB Logic board and SMB8 module board

less modules and power supply.

BIO16 16 Position BASIC I/O Unit Includes SLB logic board and SMB16 module board

less modules and power supply.

Warranty: duTec warrants its products to be free of defects in materials and

workmanship for a period of two (2) years from date of shipment.
DuTec may, at its option repair or replace all materials found to be
defective. All repair or replacement must be performed by duTec
personnel. Any parts determined by duTec to be defective as a result
of abuse, attempts to repair, or misuse by the customer will be repaired
at the expense of the customer.

1-11(Vol.1)

NOTES

The Basic I/O 1

1-12(Vol.1)

Setup & Installation 2

MOUNTING:

BASIC I/Os come in 4, 8, and 16 channel versions. Figure 2-1 below shows the footprint of

each BASIC I/O. Using corner holes, the unit can be mounted with 4- #6 or #8 round head or
pan head screws. The BIO16 version has two additional mounting holes located near the
center of the board as well. Hole locations in relation to the overall dimensions for each are
shown below. Since the same BASIC I/O boards are used for digital or analog applications,
the same mounting dimensions and panel space are used for both.

FIGURE 2-1 BASIC I/O FOOTPRINT

2-1(Vol.1)

Setup & Installation 2

POWER WIRING:

Power connections are made at the 2 position terminal block located on the module board
marked +5V and GND No. 8 captive wire clamps accept 10-16 AWG wire or spade lugs.

+5V GND

Power wiring conventions:

+ of the power source to the +5V terminal

- of the power source to the terminal marked GND

Power requirements

Voltage: 5.0- 5.4Vdc
Current: 250 mA + 25mA per digital module or 250 + 200mA per analog

module.

Note that the current draw of some specialized digital
modules such as the IDC5S or the IDC5Z, can be
substantially larger than 25 mA. Consult the specific
module data sheet for this value when sizing power
supplies.

Practices: In general it is good practice to reserve the +5Vdc power supply

exclusively for the task of powering one or more BASIC I/O units. As
with any microprocessor based equipment, reasonably clean power is
required for reliable operation. Sharing power with other devices such
as field signal transducers and contact excitation should be avoided.

2-2(Vol.1)

Setup & Installation 2

COMMUNICATING WITH THE BASIC I/O:

The BASIC I/O is designed to serve as an intelligent I/O front end for a Host computer
(Typically a P.C.). The host and BASIC I/O communicate over a serial link. This interchange
is half-duplex in nature; that is to say the host and BASIC I/O will never be transmitting at
the exact same time. Further, the communications protocol is considered “speak-only-when­spoken-to”; the Host must poll the BASIC I/O whenever it needs fresh data. This polling is
accomplished when the host sends an instruction to the BASIC I/O. The BASIC I/O will then
generate a reply. Each valid instruction will illicit a corresponding response. The integrity of
this communication is verified using message content checksums.

The serial communication is a form of ASCII printable characters and makes heavy use of the
hexadecimal numbering system. The format of the ASCII characters used is: One start bit,
eight data bits, one stop bit, and no parity.

2-3(Vol.1)

Setup & Installation 2

BASIC I/Os can be networked together to obtain up to 4096 I/O points of data. These serial
networks can be either multidrop or repeat.

Figure 2-3 Multidrop V.S. Repeat networks

Multidrop:

Multidrop networks can be up to 5000 ft long end-to-end.

Each station is passively located on the network and represents one “Drop” or
load to the host communication driver.

A multidrop network will tolerate loss of power to any one station without
effecting the rest of the network..

RS-485 can only be multidrop

Signal boost may be necessary depending on line conditions and number of
drops.

Repeat:

Repeat networks can be as long as 5000 ft between each unit.
Each station plays an active role in communications to other units. If power is
removed from a unit in a repeat network, communications to units “downstream”
from it will be lost as well.

2-4(Vol.1)

Setup & Installation 2

The serial communications link between a Host computer and a network of BASIC I/Os is
made up of either a single (RS-485 half-duplex) or Dual (RS-422 full duplex) shielded twisted
pair (s) of wires whose shields are connected to a signal common conductor. This
communications link should in turn have an overall shield which is isolated from the signals
(including signal ground) and connected to earth or chassis ground at one location. The most
common cause of difficulty experienced by customers in the field is improperly installed
communications wiring.

RS-422:

Advantages:

Easier to implement in software since host driver need not be controlled.

Can be either Multidrop or Repeat

No turn-around delay required.

Disadvantages:

Requires five conductor wire instead of three

RS-485:

Advantages

Needs only 3 wire conductor

Disadvantages:

:

Host 485 driver control must be implemented requiring tricky serial port manipulations

Can only be Multidrop

Usually requires turn around delay implementation.

2-5(Vol.1)

Setup & Installation 2

RS-485 Programming:

The BASIC I/O will work equally well when connected to either RS-422 or RS-485.
However special host programming considerations may be necessary when implementing an
RS-485 network. Unlike RS-422 where both the transmit and Receive signals have their own
differential pair of conductors, RS-485 utilizes only one
conductors is used bidirectionally and handles both transmit and receive signals. In order for
this to be possible, the transmitter for each device on this type of network must be enabled and
disabled whenever a message is to be sent. The transmitter for the BASIC I/O is designed to
handle this control automatically. However, the transmitter control for most popular RS-485
cards that are installed in the Host computer must be controlled by the user program. This
control is not straight forward and may impact the overall system throughput with inherent
delay periods. The following is a typical instruction/ response transaction between a host
computer and a BASIC I/O using RS-485.

1) The Host computer enables its RS-485 transmitter (usually via the RTS line)

2) The Host then sends an instruction to the BASIC I/O in the form of an ASCII printable
string.

3) Once the Host determines that the string has been completely sent, the RS-485
transmitter is disabled.

4) Every BASIC I/O on the network receives the instruction and begin to decode it. That
particular BASIC I/O addressed begins to construct a response.

differential pair. The single pair of

5) Once the carriage return is of the instruction is received, the BASIC I/O begins to
transmit a response.

6) The Host receives the response and takes the appropriate action.

This interaction is heavily dependant on asynchronous timing. Usually, the Host software has
no real means of determining that the instruction has been completely sent. This means that
the program must calculate the

2-6(Vol.1)

Setup & Installation 2

approximate time necessary to transmit the entire instruction before the RS-485 driver is
disabled. Since the BASIC I/O can respond very quickly to the instruction, the Host must
disable the driver as soon as possible in order to receive the BASIC I/Os response. RS-485
communications can be tricky at best and should be seriously considered before being
adopted. Third party software users should make sure that the package they have chosen
supports the particular RS-485 communications card to be used.

COMMUNICATION WIRING:

The Host to first BASIC I/O can be RS-422 or RS-485. Most Host computers come
equipped with an RS-232 serial port. A choice must be made to either equip the host with an
RS-422 or RS-485 card or to use an external RS-232 to RS-422/ 485 converter.

For ranges less than 5000 feet, both RS-422 and RS-485 networks can operate in multidrop
mode. For ranges greater than 5000 feet, RS-422 (NOT RS-485) networks can operate in
repeater mode. In this mode, the distance between individual units can be up to 5000 feet. The
trade-off for using the repeat mode is that the powering down of any single unit disables
communications with all units further “downstream” from the host.

A network of BASIC I/O’s must be made up of units which are configured as either all
multidrop or all repeat.

2-7(Vol.1)

Setup & Installation 2

Network load V.S. Noise suppression:

In order to improve RS-485 Bus noise immunity, particularly under tri-state conditions, a pair
of “Network Bias Resistors” have been installed in each BASIC I/O unit. This design feature
has been implemented in order to satisfy the majority of our customers. If it is necessary to
multidrop more than eight BASIC I/O units(but ultimately less than thirty-two devices), It
will be necessary to remove these network bias resistors so as to not exceed the maximum bus
loading. However, in order to retain noise immunity, the network bias resistors should remain
installed in at least one BASIC I/O on the network. Figure 2-4 below shows the location of
the four network bias resistors.

R34 is the 1.5k from prior +bias resistor
R35 is the 1.5k from prior - bias resistor
R36 is the 1.5k from next + bias resistor
R37 is the 1.5k from next - bias resistor

Figure 2-4 Network Bias Resistor Locations

2-8(Vol.1)