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MM300 MOTOR MANAGEMENT SYSTEM – COMMUNICATIONS GUIDE
RS485 INTERFACE (MODBUS RTU)
CHAPTER 1: COMMUNICATIONS GUIDE
Function Code 07H
Modbus Implementation: Read Exception Status
MM300 Implementation: Read Device Status
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 MM300 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 MM300 Implementation: Loopback Test
This function is used to test the integrity of the communication link. The MM300 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
0
Alarm
1
Trip
2
Internal fault
3
Auto
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