General Description (Continued)
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
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 operation without the need for a remote supervisory
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.
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.
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.
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.
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.
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:
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.
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
DIGITAL FILTER
Command
Message
($ prompt)
$1MBD
Response
Message
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.
MBD Modbus Disable
*
RD
Read Data
$1RD
*+00072.00
*0102
*31070142
*+00000.00
*
RMA Read Module Address $1RMA
RS
RZ
Read Setup
Read Zero
$1RS
$1RZ
$1WE
WE Write Enable
Write Protected Commands.
COMMUNICATIONS
CZ
RR
SU
TS
TZ
Clear Zero
$1CZ
*
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
Remote Reset
Setup Module
Trim Span
$1RR
$1SU31070142
*
*
$1TS+00600.00 *
Trim Zero
$1TZ+00000.00
$MBR01
*
*
MBR Write Slave Address
RHOPOINT [ RHOPOINT COMPONENTS ]
