GE Industrial Solutions ASTAT BP User Manual
Page 80
ASTAT BP User Manual
80
GE Industrial Solutions
©2013 GE Company All Rights Reserved
APPENDIX A -
MODBUS RTU PROTOCOL
A.1.
Introduction
This document summarizes the serial link protocol to / from the DIGITAL SOFT STARTER(ASTAT-BP).
Features:
•
RS485 Hardware.
•
Asynchronous serial link.
•
Half duplex.
•
Format: Modbus RTU Mode (Remote Terminal Unit Mode).
o Binary
o Each character contains 11 bits:
- One start bit
-8 data bits, least significant bit sent first.
- 1 Parity bit. Even / Odd / No can be selected.
- 1 Stop bit if Parity is used, 2 stop bits if Parity is not used.
o Cyclical Redundancy Check (CRC), 16 bits.
•
Baud Rates: 1200 / 2400 / 4800 / 9600 bits per second.
•
Response time of the ASTAT-BP:
o Normally, 4ms <= time response <= 40mS.
o For a long response, time response <= 200mS.
•
It is not recommended to transmit to the ASTAT-BP at a rate higher than once per second because this can
slow down ASTAT-BP response times.
•
After storing parameter settings, there is a 1 sec. time period during which transmission to the same ASTAT-
BP is forbidden.
•
Broadcast commands: not supported.
Notes:
*
It is recommended that you connect 120 OHM resistors to both ends of the serial link.
*
You must turn OFF (and ON again) power to the controller after changing Baud_Rate, Parity_Check or
Serial_Link_No (Slave Address). These parameters can only be modified manually and not through the
Serial Link.
WARNING
You must connect earth to the ASTAT-BP earth screw before connecting serial link wires.
Ignoring this instruction may result in permanent damage to the Serial Link Hardware
and might result in death or serious injury.