with string functions common to most high-level languages

such as BASIC. For computers that support standard ports

such as RS-232, no special machine language software

drivers are necessary for operation. The modules can also

be connected to auto-answer modems for long-distance

operation without the need for a remote supervisory

computer. The ASCII format makes system debugging

easy with a dumb terminal.

Because the Modbus protocol does not support echoing

D5000M RS-232 modules may not be daisy-chained. This

limits you to one four-channel module per RS-232 port.

RS-485 was developed for multidropped systems that can

communicate at high data rates over long distances. RS-

485 receivers can handle common mode voltages from -7

to +12V without loss of data, making them ideal for trans-

mission over great distances. Since an RS-485 system

cannot transmit and receive at the same time it is a half-

duplex system. For systems requiring many modules,

high speed or long distances RS-485 is recommended.

COMMAND SET

The D5000M series uses the Modbus RTU or the

DGH ASCII protocol for communication.

The Modbus RTU binary protocol uses a master-slave

technique, in which only the master device can initiate

transactions. The slave devices respond by supplying

the requested data to the master or by taking the ac-

tion requested in the query. The master can address

any slave device. The returned messages are consid-

ered response messages. The supported master

codes are:

Modbus RTU Functions and Descriptions

04 Read Input Register (Analog Inputs)

06 Preset Single Register (DGH/RTU Protocol)

The DGH ASCII protocol is a command and response

protocol using ASCII characters for easy troubleshooting

and interpretation of data values.

D5000M Series ASCII Command Set.

Command and Definition

Typical

Typical

Command

Response

Message

Message

($ prompt)

MBD Modbus Disable

$1MBD

*

RD

Read Data

$1RD

*+00072.00

RMA Read Module Address

$1RMA

*0102

RS

Read Setup

$1RS

*31070142

RZ

Read Zero

$1RZ

*+00000.00

WE

Write Enable

$1WE

*

Write Protected Commands.

CZ

Clear Zero

$1CZ

*

RR

Remote Reset

$1RR

*

SU

Setup Module

$1SU31070142

*

TS

Trim Span

$1TS+00600.00 *

TZ

Trim Zero

$1TZ+00000.00 *

MBR Write Slave Address

$MBR01

*

General Description (Continued)

The key to the DGH product concept is that the modules

are easy to use. You do not need engineering experience

in complicated data acquisition hardware. With the DGH

modules, anyone familiar with a personal computer can

construct a data acquisition system. This modular approach

to data acquisition is very flexible, easy to use and cost

effective. The modules can be mixed and matched to fit

your application. They can be placed remote from the host

and from each other.

The D5000M series is completely hardware and software-

compatible with the DGH D1000, D2000, D3000 and

D4000 series and may be mixed in any combination.

All modules are supplied with removeable screw-terminal

connectors and captive mounting hardware. The connec-

tors allow system expansion, reconfiguration or repair

without disturbing field wiring.

THEORY OF OPERATION

D5000M modules are complete four-channel data

acquisition systems. Each unit contains analog signal

conditioning circuits optimized for a specific input type. The

amplified sensor signals are converted to digital data with

a microprocessor-controlled integrating A/D converter.

Offset and gain errors in the analog circuitry are continu-

ously monitored and corrected using microprocessor

techniques. The D5000M converts the digital signal data

into engineering units using look-up tables. The resultant

data is stored in ASCII format in a memory buffer. The

modules continuously convert data at the rate of 8

conversions per second and store the latest result in the

buffer.

Host processors may request data by sending a query

to the module. The D5000M will instantly respond by

communicating the memory buffer data back to the

host processor. Up to 247 modules may be linked to a

single RS-485 port or one module to a RS-232C port.

Each module on a serial line is identified by a unique

user-programmable address. This addressing tech-

nique allows modules to be interrogated in any order.

DIGITAL FILTER

The D5000M options include a unique programmable

single pole digital filter. The filter is used to smooth analog

data in noisy environments. Separate time constants may

be specified for small and large signal changes. Typically a

large time constant is specified for small signal changes to

filter out noise and provide stable output readings. A

smaller time constant may be chosen for large signal

changes to provide fast response to such changes.

COMMUNICATIONS

The D5000M are designed to be easy to interface to all

popular computers and terminals. All communications to

and from the module are performed with printable ASCII

characters. This allows the information to be processed