Manual 26710V1
ProTechTPS Total Protection System
Woodward
87
Monitor and Control
If a Modbus port’s “Enable Write Commands” setting is configured “Yes”, the
respective ProTechTPS module will accept “write” commands from an external
master device (DCS, etc.). This allows a Modbus compatible device to monitor all
read registers and issue “Reset” and “Start/Abort Test Routines” commands only.
Modbus ports are independent of each other, and can be used simultaneously.
To ensure that a Modbus command to trigger a module test is valid, both “Initiate
Test” and “Confirm Test” commands must be received to initiate a test routine. A
Confirm must be received within 10 seconds of the Initiate command; otherwise,
the sequence must be re-initiated. The ProTechTPS is designed to allow only
one module to be tested at a time. Thus a module will only accept an Initiate Test
command and perform the requested test if all three modules are healthy, not
tripped, not in a test mode, and optionally not in alarm.
Modbus Communication
Each ProTechTPS Modbus communications port is designed to function as a
slave device on a Modbus network using the industry-standard Modbus RTU
(remote terminal unit) transmission protocol. For more information on Modbus
networks and the RTU transmission protocol, refer to Modbus Protocol
Reference Guide PI–MBUS–300 Rev. J.
A Modbus function code tells the addressed slaves what function to perform. The
following table lists the function codes supported by the ProTechTPS:
Code Definition
Reference
Address
02
Boolean Read (Read Input Status)
1XXXX
(Status of Alarms/Shutdowns, Discrete input/outputs)
04
Analog Read (Read Input Registers)
3XXXX
(Speed, Acceleration, etc)
05
Boolean Write (Force Single Coil)
0XXXX
(Reset and Test Initiate Commands)
08
Loopback Diagnostic Test – Diagnostic code 0 only
Table 4-2. Supported Modbus Function Codes
As a slave Modbus device, the ProTechTPS is not responsible to sense or
annunciate Modbus link communication errors. However, for troubleshooting
purposes, the ProTechTPS will display a “Link Error” message in its “Monitor
Modbus” screen if a Modbus transaction request is not received within its five-
second time-out period. This error message is automatically cleared when
Modbus communications are re-established.
Port Adjustments
Before the ProTechTPS can communicate with the master device, the
communication parameters must be verified to match the master device’s
protocol settings. For security purposes, these parameters can only be set in the
module’s Configuration mode.
