GE Industrial Solutions ASTAT XT - Manual (Page 86)

86 • Appendix A - MODBUS RTU Protocol
APPENDIX A - MODBUS RTU PROTOCOL
A.1. Introduction
This document summarizes the serial link protocol to / from the DIGITAL SOFT STARTER(ASTAT-XT).
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-XT:
o
Normally, 4ms <= time response <= 40mS.
o
For a long response, time response <= 200mS.
• It is not recommended to transmit to the ASTAT-XT at a rate higher than once per second because this can slow
down ASTAT-XT response times.
• After storing parameter settings, there is a 1 sec. time period during which transmission to the same ASTAT-XT 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-XT 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.