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8 MM200 MOTOR MANAGEMENT SYSTEM – COMMUNICATIONS GUIDE
RS485 INTERFACE (MODBUS RTU) COMMUNICATIONS GUIDE
This is a function used to quickly read the status of a selected device. A short message
length allows for rapid reading of status. The status byte returned will have individual bits
set to 1 or 0 depending on the status of the slave device. For this example, consider the
following MM200 general status byte:
The master/slave packets have the following format:
Table 5: Function code 7 bitmask
Table 6: MASTER/SLAVE PACKET FORMAT FOR FUNCTION CODE 07H
Function Code 08H Modbus Implementation: Loopback
Test MM200 Implementation: Loopback Test
This function is used to test the integrity of the communication link. The MM200 will echo
the request.
For example, consider a loopback test from slave 17:
Table 7: MASTER/SLAVE PACKET FORMAT FOR FUNCTION CODE 08H
Bit Function
0Alarm
1Trip
2 Internal fault
3Auto
4 Contactor A
5 Contactor B
6 Contact output 3
7 Drive available (communications control)
MASTER TRANSMISSION BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message for slave
17
FUNCTION CODE 1 07 read device status
CRC 2 4C 22 CRC error code
SLAVE RESPONSE BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message from
slave 17
FUNCTION CODE 1 07 read device status
DEVICE STATUS (see
definition above)
1 2C status = 00101100
(in binary)
CRC 2 22 28 CRC error code
MASTER TRANSMISSION BYTES EXAMPLE DESCRIPTION
SLAVE ADDRESS 1 11 message for slave
17
FUNCTION CODE 1 08 loopback test
DIAG CODE 2 00 00 must be 00 00
DATA 2 00 00 must be 00 00
CRC 2 E0 0B CRC error code