Liquid Controls SP4000 User Manual

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105

SP4000 Flow Computer

9. RS-485 Serial Port (optional)

9.1 RS-485 Port Description:

The SP4000 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 flow 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 SP4000 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.

9.4 SP4000 RS-485 Port Pinout

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

RS-232

RS-485

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

SP4000 RS-485 Option

with Modbus RTU Protocol
manual for complete details of
RS-485