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FC-21 Flow Computer
10. RS-485 Serial Port (optional)
10.1 RS-485 Port Description:
The FC-21 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, Density, Setpoints, Month, Day, Year, Hour,
Minutes, Seconds, etc.
Accessing System Alarms
System, Process, Self Test, Service Test Errors
Accessing Totalizers
Totalizer and Grand Totalizer
Executing Various Action Routines
Reset Alarms, Reset Totalizers, Print Transaction, Reset Error History,
Start, Stop, Clear
10.2 General
The optional RS-485 card utilizes Modbus RTU protocol to access a variety of pro-
cess parameters and totalizers. In addition, action routines can be executed. For
further information, contact factory and request RS-485 Protocol manual for FC-21.
10.3 Operation of Serial Communication Port with PC
The flow computer's RS-485 channel supports a number of Modbus RTU com-
mands. 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 FC-21 then responds to these information and command requests.
Process variables and totalizers are read in register pairs in floating 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.
10.4 FC-21 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 (-)
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RS-232 RS-485