Tektronix M3000,M4000 Series Computer To Analog Output Interfaces User's Manual 64990A User manual

M3000/M4000 Series

User’s Manual

A GREATER MEASURE OF CONFIDENCE

WARRANTY

Hardware

Keithley Instruments, Inc. warrants that, for a period of one (1) year from the date of shipment (3 years for Models 2000, 2001, 2002, 2010 and 2700), the
Keithley Hardware product will be free from defects in materials or workmanship. This warranty will be honored provided the defect has not been caused
by use of the Keithley Hardware not in accordance with the instructions for the product. This warranty shall be null and void upon: (1) any modification of
Keithley Hardware that is made by other than Keithley and not approved in writing by Keithley or (2) operation of the Keithley Hardware outside of the
environmental specifications therefore.

Upon receiving notification of a defect in the Keithley Hardware during the warranty period, Keithley will, at its option, either repair or replace such Keithley Hard­ware. During the first ninety days of the warranty period, Keithley will, at its option, supply the necessary on site labor to return the product to the condition prior to
the notification of a defect. Failure to notify Keithley of a defect during the warranty shall relieve Keithley of its obligations and liabilities under this warranty.

Other Hardware

The portion of the product that is not manufactured by Keithley (Other Hardware) shall not be covered by this warranty, and Keithley shall have no duty of
obligation to enforce any manufacturers' warranties on behalf of the customer. On those other manufacturers’ products that Keithley purchases for resale,
Keithley shall have no duty of obligation to enforce any manufacturers’ warranties on behalf of the customer.

Software

Keithley warrants that for a period of one (1) year from date of shipment, the Keithley produced portion of the software or firmware (Keithley Software) will
conform in all material respects with the published specifications provided such Keithley Software is used on the product for which it is intended and other­wise in accordance with the instructions therefore. Keithley does not warrant that operation of the Keithley Software will be uninterrupted or error-free and/
or that the Keithley Software will be adequate for the customer's intended application and/or use. This warranty shall be null and void upon any modification
of the Keithley Software that is made by other than Keithley and not approved in writing by Keithley.

If Keithley receives notification of a Keithley Software nonconformity that is covered by this warranty during the warranty period, Keithley will review the
conditions described in such notice. Such notice must state the published specification(s) to which the Keithley Software fails to conform and the manner
in which the Keithley Software fails to conform to such published specification(s) with sufficient specificity to permit Keithley to correct such nonconfor­mity. If Keithley determines that the Keithley Software does not conform with the published specifications, Keithley will, at its option, provide either the
programming services necessary to correct such nonconformity or develop a program change to bypass such nonconformity in the Keithley Software.
Failure to notify Keithley of a nonconformity during the warranty shall relieve Keithley of its obligations and liabilities under this warranty.

Other Software

OEM software that is not produced by Keithley (Other Software) shall not be covered by this warranty, and Keithley shall have no duty or obligation to
enforce any OEM's warranties on behalf of the customer.

Other Items

Keithley warrants the following items for 90 days from the date of shipment: probes, cables, rechargeable batteries, diskettes, and documentation.

Items not Covered under Warranty

This warranty does not apply to fuses, non-rechargeable batteries, damage from battery leakage, or problems arising from normal wear or failure to follow
instructions.

Limitation of Warranty

This warranty does not apply to defects resulting from product modification made by Purchaser without Keithley's express written consent, or by misuse
of any product or part.

Disclaimer of Warranties

EXCEPT FOR THE EXPRESS WARRANTIES ABOVE KEITHLEY DISCLAIMS ALL OTHER WARRANTIES, EXPRESS OR IMPLIED, INCLUD­ING WITHOUT LIMITATION, ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. KEI­THLEY DISCLAIMS ALL WARRANTIES WITH RESPECT TO THE OTHER HARDWARE AND OTHER SOFTWARE.

Limitation of Liability

KEITHLEY INSTRUMENTS SHALL IN NO EVENT, REGARDLESS OF CAUSE, ASSUME RESPONSIBILITY FOR OR BE LIABLE FOR: (1)
ECONOMICAL, INCIDENTAL, CONSEQUENTIAL, INDIRECT, SPECIAL, PUNITIVE OR EXEMPLARY DAMAGES, WHETHER CLAIMED
UNDER CONTRACT, TORT OR ANY OTHER LEGAL THEORY, (2) LOSS OF OR DAMAGE TO THE CUSTOMER'S DATA OR PROGRAM­MING, OR (3) PENALTIES OR PENALTY CLAUSES OF ANY DESCRIPTION OR INDEMNIFICATION OF THE CUSTOMER OR OTHERS FOR
COSTS, DAMAGES, OR EXPENSES RELATED TO THE GOODS OR SERVICES PROVIDED UNDER THIS WARRANTY.

Keithley Instruments, Inc. 28775 Aurora Road • Cleveland, Ohio 44139 • 440-248-0400 • Fax: [phone]

1-888-KEITHLEY (534-8453) • www.keithley.com

Sales Offices:BELGIUM: Bergensesteenweg 709 • B-1600 Sint-Pieters-Leeuw • 02-363 00 40 • Fax: [phone]

CHINA: Yuan Chen Xin Building, Room 705 • 12 Yumin Road, Dewai, Madian • Beijing 100029 • 8610-6202-2886 • Fax: [phone]
FINLAND: Tietäjäntie 2 • 02130 Espoo • Phone: [phone] • Fax: [phone]
FRANCE: 3, allée des Garays • 91127 Palaiseau Cédex • 01-64 53 20 20 • Fax: [phone]
GERMANY: Landsberger Strasse 65 • 82110 Germering • 089/84 93 07-40 • Fax: [phone]
GREAT BRITAIN: Unit 2 Commerce Park, Brunel Road • Theale • Berkshire RG7 4AB • 0118 929 7500 • Fax: [phone]
INDIA: Flat 2B, Willocrissa • 14, Rest House Crescent • Bangalore 560 001 • 91-80-509-1320/21 • Fax: [phone]
ITALY: Viale San Gimignano, 38 • 20146 Milano • 02-48 39 16 01 • Fax: [phone]
JAPAN: New Pier Takeshiba North Tower 13F • 11-1, Kaigan 1-chome • Minato-ku, Tokyo 105-0022 • 81-3-5733-7555 • Fax: [phone]
KOREA: 2FL., URI Building • 2-14 Yangjae-Dong • Seocho-Gu, Seoul 137-888 • 82-2-574-7778 • Fax: [phone]
NETHERLANDS: Postbus 559 • 4200 AN Gorinchem • 0183-635333 • Fax: [phone]
SWEDEN: c/o Regus Business Centre • Frosundaviks Allé 15, 4tr • 169 70 Solna • 08-509 04 679 • Fax: [phone]
SWITZERLAND: Kriesbachstrasse 4 • 8600 Dübendorf • 01-821 94 44 • Fax: [phone]
TAIWAN: 1FL., 85 Po Ai Street • Hsinchu, Taiwan, R.O.C. • 886-3-572-9077• Fax: [phone]

4/02

M3OOU/M4UUU

SERIES

USER’S

MANUAL

New Contact Information

Keithley Instruments, Inc.

28775 Aurora Road

Cleveland, OH 44139

Technical Support: 1-888-KEITHLEY

Monday – Friday 8:00 a.m. to 5:00 p.m (EST)

Fax: [phone]

Visit our website at http://www.keithley.com

Part Number: 24809

Revision Level:

First Printing: March

A

1989

Copyright

WARNING

MetraByte Corporation assumes no liability for damages consequent

product. This product is not designed

in life support

All

rights reserved.

transmitted, in any form by any means, electronic. mechanical, photocopying, recording. or

otherwise, without the express

Information furnished by MetraByte Corporation

However,

infringements

granted by implication

No

no

responsibility

of

patents

part

of

this publication may

or

is

other rights of third parties which may result from

or

otherwise under any

with

prior

assumed

or

wriien permission

by

0

1989

to

its

the use

use;

its

components of a level of retiabi[ity suitable for use

critical applications.

be

reproduced. stored in a retrieval system. or

of

MetraByte Corporation.

is

believed

MetraByte Corporation

patent

tights

to

be accurate and reliable.

for

of

MetraByte Corporation.

of

nor for any

use.

No

this

license is

M3000/M4000 modules are not intrinsically safe devices and should not

environment unless enclosed in approved explosion-proof housings.

a

IBMB

PC/XT/AT

MetraBytem is

is

a

registered trademark

trademark

of

MetraByte Corporation.

of

International Business Machines Corporation.

be

used in an explosive

Safety Precautions

The following safety precautions should be observed before using
this product and any associated instrumentation. Although some in­struments and accessories would normally be used with non-haz­ardous voltages, there are situations where hazardous conditions
may be present.

This product is intended for use by qualified personnel who recog­nize shock hazards and are familiar with the safety precautions re­quired to avoid possible injury. Read and follow all installation,
operation, and maintenance information carefully before using the
product. Refer to the manual for complete product specifications.

If the product is used in a manner not specified, the protection pro­vided by the product may be impaired.

The types of product users are:

Responsible body is the individual or group responsible for the use

and maintenance of equipment, for ensuring that the equipment is
operated within its specifications and operating limits, and for en­suring that operators are adequately trained.

Operators use the product for its intended function. They must be

trained in electrical safety procedures and proper use of the instru­ment. They must be protected from electric shock and contact with
hazardous live circuits.

Maintenance personnel perform routine procedures on the product

to keep it operating properly, for example, setting the line voltage
or replacing consumable materials. Maintenance procedures are de­scribed in the manual. The procedures explicitly state if the operator
may perform them. Otherwise, they should be performed only by
service personnel.

Service personnel are trained to work on live circuits, and perform

safe installations and repairs of products. Only properly trained ser­vice personnel may perform installation and service procedures.

Keithley products are designed for use with electrical signals that
are rated Installation Category I and Installation Category II, as de­scribed in the International Electrotechnical Commission (IEC)
Standard IEC 60664. Most measurement, control, and data I/O sig­nals are Installation Category I and must not be directly connected
to mains voltage or to voltage sources with high transient over-volt­ages. Installation Category II connections require protection for
high transient over-voltages often associated with local AC mains
connections. Assume all measurement, control, and data I/O con­nections are for connection to Category I sources unless otherwise
marked or described in the Manual.

Exercise extreme caution when a shock hazard is present. Lethal
voltage may be present on cable connector jacks or test fixtures. The
American National Standards Institute (ANSI) states that a shock
hazard exists when voltage levels greater than 30V RMS, 42.4V
peak, or 60VDC are present. A good safety practice is to expect

that hazardous voltage is present in any unknown circuit before
measuring.

Operators of this product must be protected from electric shock at
all times. The responsible body must ensure that operators are pre­vented access and/or insulated from every connection point. In
some cases, connections must be exposed to potential human con­tact. Product operators in these circumstances must be trained to
protect themselves from the risk of electric shock. If the circuit is
capable of operating at or above 1000 volts, no conductive part of

the circuit may be exposed.

Do not connect switching cards directly to unlimited power circuits.
They are intended to be used with impedance limited sources.
NEVER connect switching cards directly to AC mains. When con­necting sources to switching cards, install protective devices to lim­it fault current and voltage to the card.

Before operating an instrument, make sure the line cord is connect­ed to a properly grounded power receptacle. Inspect the connecting
cables, test leads, and jumpers for possible wear, cracks, or breaks
before each use.

When installing equipment where access to the main power cord is
restricted, such as rack mounting, a separate main input power dis­connect device must be provided, in close proximity to the equip­ment and within easy reach of the operator.

For maximum safety, do not touch the product, test cables, or any
other instruments while power is applied to the circuit under test.
ALWAYS remove power from the entire test system and discharge
any capacitors before: connecting or disconnecting cables or jump­ers, installing or removing switching cards, or making internal
changes, such as installing or removing jumpers.

Do not touch any object that could provide a current path to the com­mon side of the circuit under test or power line (earth) ground. Always
make measurements with dry hands while standing on a dry, insulated
surface capable of withstanding the voltage being measured.

The instrument and accessories must be used in accordance with its
specifications and operating instructions or the safety of the equip­ment may be impaired.

Do not exceed the maximum signal levels of the instruments and ac­cessories, as defined in the specifications and operating informa­tion, and as shown on the instrument or test fixture panels, or
switching card.

When fuses are used in a product, replace with same type and rating
for continued protection against fire hazard.

Chassis connections must only be used as shield connections for
measuring circuits, NOT as safety earth ground connections.

If you are using a test fixture, keep the lid closed while power is ap­plied to the device under test. Safe operation requires the use of a
lid interlock.

5/02

If or is present, connect it to safety earth ground using the
wire recommended in the user documentation.

!

The symbol on an instrument indicates that the user should re­fer to the operating instructions located in the manual.

The symbol on an instrument shows that it can source or mea­sure 1000 volts or more, including the combined effect of normal
and common mode voltages. Use standard safety precautions to
avoid personal contact with these voltages.

The WARNING heading in a manual explains dangers that might
result in personal injury or death. Always read the associated infor­mation very carefully before performing the indicated procedure.

The CAUTION heading in a manual explains hazards that could
damage the instrument. Such damage may invalidate the warranty.

Instrumentation and accessories shall not be connected to humans.
Before performing any maintenance, disconnect the line cord and

all test cables.

To maintain protection from electric shock and fire, replacement
components in mains circuits, including the power transformer, test
leads, and input jacks, must be purchased from Keithley Instru­ments. Standard fuses, with applicable national safety approvals,
may be used if the rating and type are the same. Other components
that are not safety related may be purchased from other suppliers as
long as they are equivalent to the original component. (Note that se­lected parts should be purchased only through Keithley Instruments
to maintain accuracy and functionality of the product.) If you are
unsure about the applicability of a replacement component, call a
Keithley Instruments office for information.

To clean an instrument, use a damp cloth or mild, water based
cleaner. Clean the exterior of the instrument only. Do not apply
cleaner directly to the instrument or allow liquids to enter or spill
on the instrument. Products that consist of a circuit board with no
case or chassis (e.g., data acquisition board for installation into a
computer) should never require cleaning if handled according to in­structions. If the board becomes contaminated and operation is af­fected, the board should be returned to the factory for proper
cleaning/servicing.

TABLE

OF

CONTENTS
Warranty
CHAPTER

CHAPTER

1

2

CHAPTER 3

CHAPTER

CHAPTER

CHAPTER

CHAPTER
CHAPTER

CHAPTER
CHAPTER

Appendix
Appendix

4

5

6

7

8
9

10

A

B

4

Getting Started

Terminal Designations 1-1

Default

Quick

Mode

Hook-Up

1-2

1-3

Functional Description

Block

Diagram 2-3

Communications

RS-232C 3-2

Multi-party Connection 3-3
Software Considerations 3-4

Changing Baud Rate

RS-485

3-6

3-5

RS-485 Multidrop System 3-7

Command

Table

User

Commands

Error Messages

Set

of

Commands

4-6

4-7

4-20

Setup Information and Command

Command Syntax 5-2
Setup Hints

Digital

110

Manual ModedDigital
Controller Input
Limit Switches

Power

Supply

5-9

Function

6-4

6-5

Inputs

6-1

Troubleshooting
Cali brat

M4000

Slope Control

Input Data Scaling

Watchdog Timer
Analog Readback

(ASCII TABLE
M3000/4000

ion

Features

10-1

)

Data

10-4

10-6

10-7

Sheet

3

WARRANTY

MetraByte warrants each
in materials and workmanship under normal conditions of use and service and will
replace any component

tation charges prepaid within one year

no liability, expressed or implied, beyond its obligation to replace any component
involved. Such warranty is in lieu of

WARNING

The

circuits and software contained in

proprietary. Purchase of these products does not transfer any rights
any license to

the

circuits or software used
or decompiling of the software program
of the software program by any means

As

explained in the setup section, all setups are performed entirely from the

outside of the

M3000/4000

M3000

found

and M4000 series module to be free from defects

to be defective, on its return

of

its original purchase. MetraByte assumes

all

other warranties expressed or implied.

M3000

and

to

M4000

MetraByte, transpor-

series modules are

or

in

these products. Disassembling

is

explicitly prohibited. Reproduction

is

illegal.

module. There

is

no need to open the module

grant

because there are no user-serviceable parts inside. Removing the cover or

tampering with, modifying, or repairing by unauthorized personnel

matically void the warranty. MetraByte

tial

damages.

is

not responsible for any consequen-

will

auto-

RETURNS

When returning products
Authorization Number and shipping instructions. Write the Return Authorization

Numberon the outside ofthe shipping box. MetraBytestrongly recommendsthat you
insure the product
they will not

be

for

accepted.

for

any

reason, contact the factory and request a Return

value prior to shipping. ttems should not

be

returned collect as

4

Chapter

1

Getting

Introduction

The MetraByte

analog output interfaces. They are designed to

computer and communicate with standard
ASCII commands are used to control
which is scaled to provide commonly used current and voltage ranges. An on-board

microprocessor is used

gent analog output functions.

M3000

sensitive applications where some

M3000

read back.

M4000

enhancements

versions provide a basic computer-to-analog output interface for cost­units feature step-function outputs, fixed input scaling, and no analog

versions perform alI

M3000/4000

to

:

is a series of completely self-contained computer-to-

be

mounted remotely from a host

RS-232

a

1

2-bit

provide the communications interface and many intelli-

of

the intelligent enhancements are not required.

of

the

M3000

functions plus many additional intelligent

and

DAC

RS-485

(Digital-to-Analog Converter)

serial ports. Simple

Started

Controlled output slew rates
True analog readback

Programmable input data scaling
Programmable starting value

Watchdog timer
This manual has been written

Basic operating characteristics
noted, the information in this manual applies to both versions. Commands and

functions exclusive

Terminal Designations

All

M3000

slight variations between currentholtage and

Pin

1

Pin

2

Pins 1 and 2 are the connections
input data is scaled

Voltage outputs can source or sink current.

and

+I

-I

to

M4000

OUT or

OUT

or

so

the

units have similar terminal designations, although there are

+V

-V OUT

that the voltage at

to

of

M4000

OUT

to

be a guide for both the M3000 and

both models are identical and unless otherwise

are

so

noted in the text.

RS-232/RS-485

the analog output signal. On voltage models, the

+V

OUT

is

positive with respect to -V OUT.

models.

M4000

units.

1-2

M3000/4000 USERS

MANUAL

On current output models, the output current flows from the

-I

OUT

terminal,
positive voltage level than the
current.

Pins 1 and 2 are electrically isolated from the other pins.
Pin

3

Pin 4
Pin

5

Pins 3-5 are digital input pins. They may be used as general-purpose inputs
may be set-up to provide special functions that control the analog output. The

standard factory set-up configures the
down control

negative true. A full functional description
Pin 6

Grounding this pin places the module in Default Mode, described in detail below.
Pin

7

Pin

8

Pins 7 and 8 are connections to the serial communications lines connecting the
module to the host computer or terminal.

so

for a typical resistive load, the

-1

OUT

terminal. Current outputs can only source

D12
DI 1 /UP*

DIO/DN*

UP*

and

of

the analog output. The * designation indicates that the labels are

of

DEFAULT*

TRANSMIT

RECEIVE

or

or

DATA*

DATA

+I

OUT

DN*

pins to provide manual up and

these pins may be found in Chapter

+I

OUT terminal

terminal will be at a more

to

or

the

they

6.

On RS-232 models, the TRANSMIT pin

module. The RECEIVE pin

On RS-485 versions,
communications lines.

respectively.

Pin

9

Pin

1OGND

Pins 9 and

30V unregulated power.

Default

All

M3000/4000

Read Only Memory)

EEPROM

rate, address, parity, etc.

tion is retained even

necessary to open the module case.

The

EEPROM

parameters may be configured remotely through the communications port without
having

drawback in using EEPROM instead

to

V+

10

are the powerconnections. The M3000/4000 modules operate on

Mode

modulescontain an EEPROM (Electrically Erasable Programmable

replaces the usual array

provides tremendous system flexibility since

physically change switch and pot settings. However, there

DATA

is

the serial input into the module.

and

DATA*

DATA

to

and

DATA*

store setup information and calibration constants. The

of

The

memory is nonvolatile which means that the informa-

if

power is removed.

is

the serial output connection from the

are connections to the balanced

are sometimes labeled

switches and pots necessary to specify baud

No

batteries are used

of

switches; there is no visual indication of the

DATA+

so

all

of the module’s setup

RS-485

and

DATA-

it

is never

is

one minor

10-

Getting Started

setup information in the module. It is impossible to tell just by looking at the module

what the baud rate, address, parity and other settings are.

communications with a module whose address and baud rate are unknown.

overcome this, each module has an input pin labeled DEFAULT*. By connecting this

pin to Ground, the module is put in a known communications setup called Default

Mode.

It

is difficult to establish

1-3

To

The Default Mode setup

Grounding the DEFAULT* pin

The setup may

of

the setups stored in the module. In Default Mode, all commands are available.

A

module in Default Mode will respond

included in every command for proper responses. The

address may be read back with the

address character is to deliberately generate an error message. The error message

outputs the module’s address directly after

Setup information

Baud rate and parity setups may be changed without affecting the Default values of

300

baud and no panty. When the DEFAULT* pin is released, the module automati-

cally performs a program reset and configures itself to the baud rate and parity stored

in the setup information.

The Default Mode

orcomputer forthe purpose

a

module

RS-232

Software

that you begin to get familiar with the module by setting

using a dumb terminal or a computer that acts like a dumb terminal. Make the

connectionsshown inthequick hook-updrawings, Figures

in the Default Mode

communications package on yourcornputerto put

this step varies from computer

inst ructions.

in

&

is

be

read back with the Read Setup

in

is

Default Mode may not be used in a string with other modules.

RS-485

not required

Quick

is:

300

baud, no parity, any address is recognized.

does

not change any of the setupsstored in EEPROM.

(RS)

a

module may

intended to

of

identifying and modifying setupvalues. In most cases,

command

to

any address. A dummy address must be

ASCII

RS

command. An easy way to determine the

the

“?”

prompt.

be

changed at will with the Setup

be

used with asingle module connected toaterminal

to

determine

value of the module

(SU)

command.

Hook-Up

to

begin using your

by

grounding the DEFAULT* terminal. Initialize the terminal

to

computer, refer to your computer manual

M3000/4000

it

it

into the “terminal” mode. Since

module. We recommend

up on the bench. Start by

1.1

or

1.2.

Putthe module

all

far

Connect a suitable voltmeter or ammeter to the output connections

monitor the output signal.

current-output modules, a sense resistor and a voltmeter may be used as shown in

Fig.

1.1.

Turn power on

connector. The output signal should increase in value as the UP* pin

release the UP* pin and ground the DN* (down) pin. The output signal should

decrease in value as the pin

If

an ammeter

to

the module. Momentarily ground the UP* pin on the

is

held

is

not available

low.

to

measure the signals from

of

the module to

is

held

low.

Now

1-4

M3000/4000

USERS

MANUAL

This demonstrates the “Manual Mode” method

quick check to see if the module

Use your terminal to type the command

is

connected and working properly.

$1

RD

of

controlling the output. It is also

and

terminate the command with a

a

carriage return. The module will respond with an * followed by the output data

reading. The data includes sign, seven digits and a decimal point. For example, a

typical reading might be

*+00015.00.

This is an output status reading and it should

closely correspond with the reading on your meter.

Now

type the command:

$1

A0+00010.00

The module should respond with

rnilliamps). This demonstrates the Analog Output

primary method

If

you have a voltage output module,try these commands:

$1

A0+00000.00

$1

AO+OOlOO.OO

$1

A0+01000.00

$1

A0+01234.00

and terminate with a carriage return.

I*’

and the output will change to

of

controlling the analog output.

(terminate with a carriage return)

(AO)

command, which

10

millivolts

is

(or

the

Far current output models these commands are more appropriate:

$1

A0+00004.00

$1

A0+00020.00

$1

A0+00010.00

Remember to terminate each command with a carriage return.
Once you have a response from

the

module

you

can turn

to

the Chapter 4 and get

familiar with the command set.

All

modulesareshippedfromthefactory

of

1,

300

baud

delay. Refer

rate,

no

to

the Chapter

linefeeds, no parity, limits off, no echo and two-character

5

to

configure

with asetupthat includesachanneladdress

the

module to your application.

Getting

Started

1-5

-f--l

Current

Output

Ammeter

Figure

voltmeter

1.1

RS-232C

YQkqe

Output

Quick

M

3QQQ

Analog

Output

RS232C

Hook-Up.

Cumnt
Output Output

Ammeter

Voltwe

voltmeter

FIGURE

1.2

RS-485

Quick

Hook-UP.

1-6

M3000/4000

USERS MANUAL

RS-485

An

Quick

RS-485

Hook-up

to a RS-232

port

module may be easily interfaced to an RS-232C terminal for evaluation

purposes. This connection is only suitable for benchtop operation and should never
be used for a permanent installation. Figure
will work provided the RS-232C transmit output
and the

and

RS-232C

1489

receive threshold is greater than

style interface

IC’s

will satisfy this requirement. With this connection,
characters generated by the terminal
characters, the IocaI echo

If

the current limiting capability

1

kQ

resistor in series with the RS-232C output.

Cumnt

Output

on

the terminal should be turned

of

the RS-232C output is uncertain, insert a

Ydtqe

Output

1.3

shows the hook-up.

is

current limited to less than 50mA

OV.

will

be echoed back.

This

connection

All terminals that use

To

avoid double

off.

100

1488

to

-i-b

Ammeter

Vottmeter

FIGURE

1.3

RS-485

Quick

Hook-Up

using

an

RS-232

Port.

Chapter

2

Functional Description

The MetraByte

analog process control signals in response to simple digital commands from a host

computer. The M3000/4000 units are completely self-contained and are designed to

be

operated remotely from the host. Digital commands are transmitted to the M3000/

4000

units using standard RS-232 or RS-485 communications links. Commands and

responses are in the form

The

ASCII

modems as well as intelligent controllers and computers.
Figure2.1 shows afunctional blockdiagrarn ofthe M3000/4000. The key block is the

12-bit Digital to Analog Converter (DAC). The DAC converts digital data derived from
host commands info the desired analog output. All of the other components provide

a

supporting role for proper operation

An 8-bit
the host and the DAC. The microprocessor receives commands and data from the

host computer through a serial communications
components are used to interface the microprocessor to either
communications standards. Commands received by the microprocessor are thor­oughly checked for syntax and data errors. Valid commands are then processed to

complete the desired function. A wide variety
the DAC, read status information, and to configure the module to fit the user’s

requirements. Responses to the host commands are then produced by the micropro-

cessor and transmitted back to the host over the RS-232/RS-485 serial link.

CMOS

13000/4000 Computerto Analog Output interfaces provide accurate

of

simple English ASCII character strings for ease of use.

protocol allows the units to be interfaced with dumb terminals and

of

the DAC.

microprocessor is

used

to provide an intelligent interface between

port.

Specialized communications

RS-232

of

commands are available to control

or

RS-485

An Electrically Erasable Programmable Read-only Memory (EEPROM)

retain important data even
setup information such as the address, baud rate, and parity as well
data.

In response to host commands, the microprocessor produces the appropriate digital

data necessary to control the DAC. Digital data is transmitted

opto-isolators

current that

output current is then processed and amplified by signal conditioning circuits to
produce the desired output voltage orcurrent. Output protection circuits are included

which provide electrical isolation. The DAC produces a precise analog

is

directly proportional to the magnitude of the digital data. The DAC

if

the module is powered down. The EEPROM contains

to

the

is

used to

as

calibration

DAC

through

2-2

M3000/4000

to protect the module from potentially damaging output faults.

USERS MANUAL

M4000

to monitor the output signal. The
converts the signal level to digital data. The digital data is optically isolated and may
be read by the microprocessor. This circuitry allows the M4000 user to directly
monitor the output signal and ensure its integrity.

The

the raw 1Oto30voltssupplied

It produces

232 units, the power supply produces

tions standard.

circuitry.
The power supplied

input power and communications connections. The transformer along with the opto­isoIators provide

circuitry. The isolation barrier is extremely helpful in breaking ground loops and
isolating troublesome common-mode voltages that are often found in large systems.

The isolation barrier also provides damage protection for the module and the host
in cases where the output lines may accidently contact

The combination
sor produces a very powerful system for the generation of process control signals.
The power

multidrop capability, data formatting in engineering units, limit checking, digital
calibration, and a host of other features not possible with unintelligent analog output
systems.

models also feature asimple Analog to Digital Converter (ADC) which is used

ADC

input is tied directly to the analog output and

last

major block in the diagram is the power supply. The power supply converts

bytheuserintoregulatedvoltagesusedinthe

+5V

necessary

It

also produces

to

an

isolation barrier between the output section and the rest

of

an accurate high-resolution DAC and a dedicated rnicroproces-

of

the microprocessor is used

to

operate the microprocessor and

+I5

volts to power the

the DAC and output circuitry

+1

EEPROM.

OV

necessary for the RS-232 communica-

DAC

and associated output

is

transformer isolated from the

AC

power lines.

to

provide software addressing

module.

On

RS-

of

the

for

During normal operation, the microprocessor constantly updates the

rate

of

1000 times per second, even

this characteristic to provide controlled output

are created by incrementally stepping the
precisely calculated by the microprocessor. The small output steps created at

millisecond intervals are used to approximate ramp outputs. Slope rates are
programmable and may be changed at any time with simple commands. Linear
ramps may be initialized with a single command from the host computer.
intervention or monitoring

is

required from the host; the M4000 does the rest.

if

the output

is

stable.

slew

rates. Linear output ramp signals

DAC

every millisecond with values

The

DAC

M4000

data at

fully utilizes

No

further

a

Functional

Description

2-3

Chapter

3

Communications

Introduction

The

M3000/4000

all popular computers and terminals.
are performed with printable
processed with string functions common

BASIC.

ware drivers are necessary for operation. The modules can be connected to auto­answer modems for long-distance operation without the need for a supervisory
computer. The

For computers that support

modules have been carefully designed to be easy

All

ASCII

communications

ASCII

format makes system debugging easy with a dumb terminal.

characters. This allows the information

to

most high-level languages such as

RS-232C,

no special machine language

to

and from the modules

to

interface

to

be

soft-

to

The MetraByte system

tions port with a single 4-wire cable. Up
togetheron

ten, although a string
host on a polling system; that

and must be interrogated by the host. A module can never initiate acommunications
sequence. A simple command/response protocol must be

communications collisions and
Communications

character

A

complete description of all commands is given in the Chapter

command/response sequence would

one

ASCII

cable;

to

command codes such

Command:

Response:

A

command/response sequence

The host may not initiate a new command until the
command

collisions. A valid response can be in one of three forms:

is

complete. Failure to observe this rule will result in communications

1

)

a normal response indicated by a

2)

an error message indicated by a

3)

a

communications time-out error

allows

124

of

124

multiple modules

with repeaters. A practical limit for

units is possible. The modules communicate with the

is,

the

M3000/4000

$1

RD

*+00123.00

to

be connected to a communica-

to

32

RS-485

each module responds

data

errors.

modules

as

RD

look

like this:

is

not complete until a valid response is received.

' ? '

to

' * '

prompt

are

Read

prompt

modules may be strung

RS-232C

to

its own unique address

strictly

performed with two

Data

from the analog output.

response

units is about

observed to avoid

4. A

from a previous

or

three-

typical

When a module receives a valid command,

the desired function, and then communicate the response back to the host Each

it

must interpret the command, perform

3-2

M3000/4000

command has an associated delay time in which the module is busy calculating the

response.
specified in Table

communications time-out it

error usually results when an improper command prompt or address is transmitted.

The table below lists the timeout specification for each command:

Mnemonic Timeout

DI,

HX,

ID

All other commands

If

the host does not receive a response in an appropriate amount

WE

USERS

3.1, a communications time-out error

MANUAL

is

assumed that no response data is forthcoming. This

3mS

130mS

35

mS

has

occurred. After the

of

time

Table
The timeout specification

when the module starts to transmit a response.

Data

All MetraByte modules communicate in standard

This format provides one start bit, seven data bits, one panty bit and
each character.

3.1

Response Timeout Specifications.

is

the turn-around time from the receipt

Format

of

a command to

NRZ

asynchronous data format.

one

stop bit for

RS-232C

RS-232C

between computing equipment.

to virtually all popular computers without any additional hardware. Although the

232C

MetraByte system allows for several modules to be connected
network structure.The advantages offered by the

1)

2)

3)

4) compatible with dumb terminals

is the most widely used communications standard for information transfer

RS-232C

standard

widely used by all computing equipment

no additional interface hardware in most cases

separate transmit and receive lines ease debugging

is

designed to connect a single piece

versions

of

the

M3000/4000

of

equipment to a computer, the

RS-232C

standard are:

will interface

in

a

daisy-chain

RS-

However,

1)

2)

3)

4)

5)

6)

7)

Single

Figure
Default Mode to enter the desired address, baud rate, and other setups (see Setups).

RS-232G

low

noise immunity

short usable distance

maximum baud rate

greater communications delay
less re lia ble-daisy-c hai n connection

wiring
host software must handle echo characters

is

Module

1.1

shows the connections necessaryto attach one moduleto a host. Use the

suffers from several disadvantages:

-

50

to

200

feet

-

19200

in

multiple-module systems

slightly more complex than

Connection

RS-485

Communications

3-3

The use
line.

of

echo is not necessary when using a single module on the communications

Multi-party Connection

RS-232C

4000

single communications port. The wiring necessary to create the daisy-chain isshown
in Figure
the RECEIVE input of the next module in the daisy chain. This wiring sequence must
be followed until the output of the last module in the chain is wired tathe Receive input

of

the host.

echo
address to avoid communications collisions

characters transmitted by the host are received

passed

ofthe host. Inthis
module.
command, it will respond by transmitting the response on the daisy chain network.
The response data will be ripple through any other modules in the chain until
reaches its final destination, the Receive input

is

not designed to be used in a multiparty system; however the

modules can

3.1.

Notice that starting with the host, each TRANSMIT output is wired

All

all

received data (see Setups). Each module must be setup with its own unique

on to the next station until the information

If a module in the chain is correctly addressed and receives a valid

be

daisy-chained

modules in the chain must be setup

to

allow many modules

(see

by

is

mannerallthecommandsgiven

bythe host areexamined byevery

of

to

be connected to a

to

the same baud rate and must

Setups). In this network, any

each module in the chain and

echoed backto the Receive input

the host.

M3000/

to

it

3-4

M3000/4000

The daisy chain network must be carefully implemented to avoid the pitfalls inherent

in its structure. The daisy-chain

communications link will bring down the whole system. Several rules must be

observed to create a working chain:

1.

All

wiring connections must be secure; any break

power, ground or communications breaks the chain.

2.

All

modules must be plugged into their connectors.

3. All modules must be setup for the same baud rate.

4.

All

modules must

USERS

be

MANUAL

is

aseries-connected structure and any break in the

setup for echo.

in

the wiring,

Software

If

the

messages on its Receive input along with the responses from the module. This can

be

handled by software string functions

begins with

A

properly addressed

characters in the command including the terminating carriage return. Upon receiving
the carriage return, the module will immediately calculate and transmit the response
to the command. During this time, the module will not echo any characters that

appear on its receive input. However, if a character
tation period, it will be stored in the module's internal receive buffer. This character

will be echoed after the response string is transmitted by the module. This situation

will occur

carriage return. In this case the linefeed character will be echoed after the response

string has been transmitted.

The daisy chain

in the chain receives a character
the module's internal UART. This method

nications since the UART eliminates any slewing errors caused by the transmission

lines. However, this method creates adelay in propagating the character through the

chain. The delay is equal to the time necessary to retransmit one character using the

baud rate setup in the module:

Considerations

host

device is a computer,

a

' * '

or

' ? '

if

the host computer appends a linefeed character

also

affects the command timeout specifications. When a module

it

must be able to handle the echoed command

by

character and ends

M3000/4000

module in a daisy chain will echo all of the

it

is

echoed by retransmitting the characterthrough

observing that a module response always

with a carriage return.

is

received during this compu-

on

the command

is

used to provide more reliable comrnu-

Baud Rate Delay

300

600

1200

2400

4800

9600

19200

38400

33.30 m

16.70mS

8.33mS

4.17mS

2.08mS

1.04rnS

520pS

260pS

S

Communications

3-5

One delay time is accumulated for each module in the chain. For example,
modules are used in a chain operating at 1200 baud, the accumulated delay time is

4

X

8.33

rnS

=

33.3

mS This time must

calculate the correct communications time-out error.

For modules with RS-232C outputs, the programmed communications delay speci-

fied in the setup data (see Chapter

(00)

followed by an idle line condition for one character time. This results in a delay

of two character periods. For longer delay times specified in the setup data, this
sequence

an RS-232C daisy chain since each module in the chain adds one character
communications delay.

Changing Baud

It

is possible to change the baud rate

must

1. Use the Setup

in the chain. Be careful not to generate a reset during this process. A reset can be

caused by the Remote Reset

2.

the Read Setup
same baud rate.

is

repeated. Programmed communications delay

Rate

be

done carefully to avoid breaking the communications link.

(SU)

command

(RR)

Verify that all the modules in the chain contain the new baud rate setup using

(RS)

command. Every module in the chain must be setup for the

be

added to the times listed in Table 3.1 to

5)

is implemented by sending a

is

of

an RS-232Cdaisychain on-line. This process

to

change the baud rate setup

command or power interruptions.

NULL

seldom

on

necessary in

each module

if

four

character

of

3.

Remove power from all the modules for at least 10 seconds. Restore power

to the modules. This generates a power-up reset in each module and loads in the new

baud rate.

4.

Change the host baud rate

5.

Be sure to compensate for a different communications delay as a result

new baud rate.

Using A Daisy-Chain With A Dumb

A

dumb terminal can be used to communicate

terminal is connected

commands typed into the dumb terminal
double characters when typing commands,

turn

off

the local echo. The daisy chain will provide the input command echo.

in

the same manner

to

the new value and check communications.

Terminal

to

a

daisy-chained system. The

as

a

computer used as a host. Any

will

be echoed by the daisy chain.

set

the terminal

to

full duplex mode or

To

of

the

avoid

RS-485

RS-485

rnultidropped systems that can communicate at high data rates over long distances.
RS-485 is similar
switching from 0 to
mode voltages from

transmission over great distances.

is a recently developed communications standard

to

RS-422 in that it uses a balanced differential pair of wires

5Vto

communicate

-7V

to +12V without

data.

RS-485

RS-485 receivers can handle common

loss

of

data, making them ideal for

differs from RS-422 by using one

to

satisfy the need for

3-6

M3000/4000

balanced pair of wires for both transmitting and receiving. Since an RS-485 system

cannot transmit and receive at the same time it is inherently a half-duplex system.

RS-485 offers many advantages over RS-232C:

1)

balanced line gives excellent noise immunity

2)

can communicate with MetraByte modules at 38400 baud

3)

communications distances up to

4)

true multidrop; modules are connected in parallel

5)

can disconnect modules without losing communications

6)

up

to

32 modules on one line;

7)

no communications delay due to multiple modules

8)

simplified wiring using standard telephone cable

USERS

MANUAL

10,000

124

with repeaters

feet.

RS-485 does have disadvantages.

support for this new standard. Interface boards are available for the IBM

compatibles and other

gains popularity. An
MetraByte offers interface converters

These converters also include power supplies to power up
To

expand an RS-485 system even further, repeater

MetraByte to string up to 124 modules on one communications

RS-485

Figure

that every module has a direct connection to the host system.

modules may be unplugged without affecting the remaining modules. Each module
must be setup with a unique address and the addresses can be in any order. All RS-

485

that the connector pins on each module are labelled with notations (B), (R),

(Y).

Multidrop

3.2

illustrates the wiring required for multiple-module

modules must be setup for no
This designates the colors used on standard 4-wire telephone cable:

Label Color

(6)

GND

(R)

v+

(G)

DATA* Green

(Y)

DATA Yellow

RS-485

RS-485

System

system usually requires an interface.

Black
Red

Very

few computers or terminals have built-in

PC

and

equipment will become available as the standard

to

convert RS-232C and RS-422 to

to

32

MetraByte modules.

boxes

are available from

RS-485.

port.

echo

to

avoid

RS-485

bus conflicts (see Setup).

system. Notice

Any

number

Also

note

(G),

and

of

This

color convention

cable is used, it
guarantee correct installation.

DATA* on the label is the complement

is

is

used to simplify installation.

only necessary

to

If

standard 4-wire telephone

match the labeled pins with the wire color to

of

DATA (negative true).

Co

rnmunications

3-7

I

3-8

M3000/4000

USERS

MANUAL

To minimize unwanted reflections on the transmission line, the
arranged as a line going from one module to the next. ‘Tree’

of the transmission line should be avoided. When using long transmission lines and/

or high baud rates, the data lines should be terminated at each end with
resistors. Standard values of

During normal operation, there are periods of time where all
and the communications lines are in an ‘idle’ high impedance condition. During this
condition, the lines are susceptible to noise pickup which may be interpreted as
random characters on the communications line. To prevent noise pickup, all
systems should incorporate
resistors will maintain the data lines in a ‘mark‘ condition when all drivers are

MetraByte
Special care must be taken with very long busses (greaterthan

error-free operation. Long busses must be terminated as described above. The use
of twisted cable for the

Use

parity and checksums along with the

transmission errors. In situations where many modules are used on a long line,

voltage drops in the power leads becomes an important consideration. The
wire is used both as a power connection and the common reference for the

transmission line receivers

as

acommon-mode voltage

of

-7V.

should be kept below

A1

000

series converter boxes have the

DATA

of common-mode voltage. For reliable operation, the common mode voltage

-5V.

180R

1K

in

the modules. Voltage drops in the

to

or

220Q

ohm bias resistors as shown in Figure

and

DATA*

the receivers. The receivers are rated for a maximum

are acceptable.

1

Ki2

lines will greatly enhance signal fidelity.

‘#

form

of

or

RS-485

resistors built-in.

all commands

bus

should be

random structures

200

ohm

drivers are

RS-485

3.2.

The

off.

1000

feet) to ensure

to

detect

GND

GND

leads appear

off

To avoid problems with voltage drops, modules may be powered locally rather than
transmitting the power from the host. Inexpensive ’calculator’ type power supplies
are useful in remote locations. When local supplies are used, be sure to provide a
ground reference with a third wire to the host or through a good earth ground. With
local supplies and an earth ground, only two wires for the data connections are

necessary.

Communications

All

MetraByte modules with

units of communications delay after a command has been received (see Chapter
This delay is necessary when using host computers that transmit a carriage return

as a carriage return-linefeed string. Without the delay, the linefeed character may
collide with the first transmitted character from the module, resulting

If

the host computertransmits acarriage return as a single character, the delay may

be set

to

zero to improve communications response time.

Delay

RS-485

outputs are setup at the factory to provide two

5).

in

garbled data.