GE 869 Communications Manual page 89

CHAPTER 10: MODBUS PROTOCOL
869 MOTOR PROTECTION SYSTEM – COMMUNICATIONS GUIDE
Table 10-8: Slave Packet Format for Function Code 06H
SLAVE RESPONSE
SLAVE ADDRESS
FUNCTION CODE
DATA STARTING ADDRESS
DATA
CRC
Function Code 07H
Modbus Implementation: Read Exception Status
869 Implementation: Read Device Status
The 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 has individual bits set to 1 or 0
depending on the status of the slave device. For this example, consider the following
869 general status byte:
Table 10-9: Master Packet Format for Function Code 07H
MASTER TRANSMISSION
SLAVE ADDRESS
FUNCTION CODE
CRC
Table 10-10: Slave Packet Format for Function Code 07H
SLAVE RESPONSE
SLAVE ADDRESS
FUNCTION CODE
DEVICE STATUS
(see following table)
CRC
Function code 07H includes the following bit masks:
Table 10-11: Device Table Status
Bit mask
Bit 0
Bit 1
Bit 2
Bit 3
Bit 4
Bit 5
Bit 6
Bit 7
Function Code 08H
Modbus Implementation: Loopback
869 Implementation: Loopback Test
The function is used to test the integrity of the communication link. The 869 echos the
request.
For example, consider a loopback test from slave 17:
BYTES EXAMPLE
1 11
1 06
2 04 5C
2 00 02
2 CB B9
BYTES EXAMPLE
1 11
1 07
2 4C 22
BYTES EXAMPLE
1 11
1 07
1 2C
2 22 28
Description
SP Group 3 Active
SP Group 2 Active
Pickup State
Breaker Connected
Breaker Closed
Breaker Tripped
Alarm
Trip
MODBUS PROTOCOL
DESCRIPTION
message from slave 17
store single setpoint
setpoint address 04 5C
data for setpoint address 04 5C
CRC error code
DESCRIPTION
message for slave 17
read device status
CRC error code
DESCRIPTION
message from slave 17
read device status
status = 00101100 (in binary)
CRC error code
10-5