GE Industrial Solutions MX350 Communications Guide - Manual (Page 15)

COMMUNICATIONS GUIDE RS485 INTERFACE (MODBUS RTU)
MX350 AUTOMATIC TRANSFER CONTROL SYSTEM – COMMUNICATIONS GUIDE 11
Function Code 10H Modbus Implementation: Preset Multiple Registers
MX350 Implementation: Store Multiple Setpoints
This function code allows multiple Setpoints to be stored into the MX350 memory. Modbus
“registers” are 16-bit (two byte) values transmitted high order byte first. Thus all
MX350setpoints are sent as two bytes. The maximum number of Setpoints that can be
stored in one transmission is dependent on the slave device. Modbus allows up to a
maximum of 60 holding registers to be stored. The MX350response to this function code is
to echo the slave address, function code, starting address, the number of Setpoints stored,
and the CRC.
For example, consider a request for slave 17 to store the value 00 02 to setpoint address 04
5C and the value 01 F4 to setpoint address 04 5D. After the transmission in this example is
complete, MX350 slave 17 will have the following setpoints information stored:
The master/slave packets have the following format:
Table 7: MASTER/SLAVE PACKET FORMAT FOR FUNCTION CODE 10H
Error Responses When a MX350 detects an error other than a CRC error, a response will be sent to the
master. The MSBit of the FUNCTION CODE byte will be set to 1 (i.e. the function code sent
from the slave will be equal to the function code sent from the master plus 128). The
following byte will be an exception code indicating the type of error that occurred.
Transmissions received from the master with CRC errors will be ignored by the MX350.
The slave response to an error (other than CRC error) will be:
SLAVE ADDRESS: 1 byte
FUNCTION CODE: 1 byte (with MSbit set to 1)
EXCEPTION CODE: 1 byte
Address Data
04 5C 00 02
04 5D 01 F4
MASTER TRANSMISSION BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message for slave 17
FUNCTION CODE 1 10 store setpoints
DATA STARTING ADDRESS 2 04 5C setpoint address 04
5C
NUMBER OF SETPOINTS 2 00 02 2 setpoints = 4 bytes
total
BYTE COUNT 1 04 4 bytes of data
DATA 1 2 00 02 data for setpoint
address 04 5C
DATA 2 2 01 F4 data for setpoint
address 04 5D
CRC 2 31 11 CRC error code
SLAVE RESPONSE BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message from slave
17
FUNCTION CODE 1 10 store setpoints
DATA STARTING ADDRESS 2 04 5C setpoint address 04
5C
NUMBER OF SETPOINTS 2 00 02 2 setpoints
CRC 2 82 7A CRC error code