ES749 Flow Computer
103
9. RS-485 Serial Port (optional)
9.1 RS-485 Port Description:
The ES749 has a an optional general purpose RS-485 Port which may be used for any one
of the following purposes:
Accessing Process Parameters
Rate, Temperatures, Pressures, Density, Time & Date, Setpoints, etc.
Accessing System Alarms
System, Process, Self Test, Service Test Errors
Accessing Totalizers
Heat, Mass, Corrected Volume, Volume Totalizers and Grand Totalizers
Executing Various Action Routines
Reset Alarms, Reset Totalizers, Print Transaction, Reset Error History,
9.2 General
The optional RS-485 card utilizes Modbus RTU protocol to access a variety of process
parameters and totalizers. In addition, action routines can be executed. For further information,
contact factory and request RS-485 Protocol manual.
9.3 Operation of Serial Communication Port with PC
The ow computer's RS-485 channel supports a number of Modbus RTU commands. Refer
to port pinout (below) for wiring details. Modbus RTU drivers are available from third party
sources for a variety of Man Machine Interface software for IBM compatible PC's.
The user reads and writes information from/to the RS-485 using the Modbus RTU commands.
The ES749 then responds to these information and command requests.
Process variables and totalizers are read in register pairs in oating point format. Time and
date are read as a series of integer register values. Alarms are individually read as coils. Action
routines are initiated by writing to coils.
9.4 ES749 RS-485 Port Pinout
1 Ground
2 Ground
3 Ground
4 TX/RX (+)
5 TX/RX (-)
6 Do Not Use
7 Terminating Resistor (180 Ω)
8 TX/RX (+)
9 TX/RX (-)
NOTES:
4 is internally connected to 8
5 is internally connected to 9
To terminate end of cable, connect
pin 7 to either 4 or 8.
Request ES749 RS-485 Option with
Modbus RTU Protocol manual for
complete details of RS-485
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