GE 469 Instruction Manual page 166

6.2 MODBUS FUNCTIONS
MESSAGE FORMAT AND EXAMPLE, FUNCTION 02:
The standard implementation requires the following: slave address (one byte), function code (one byte), starting digital
input (two byte), number of digital inputs to read (two bytes), and CRC (two bytes). The slave response is the slave address
(one byte), function code (one byte), byte count of digital input mask (one byte), bit mask indicating the status of requested
digital inputs (one or two bytes), and CRC (two bytes).
Note: the CRC is sent as a two byte number with the low order byte sent first.
Example 1: Request slave 11 to respond with status of digital inputs 5 to 9:
Digital Input
D1: Access
D2: Test
D3: Starter Status
D4: Emergency Restart
D5: Remote Reset
D6: Assignable Input 1
MASTER TRANSMISSION:
SLAVE ADDRESS
FUNCTION CODE
STARTING DIGITAL INPUT
NUMBER OF DIGITAL INPUTS
CRC
SLAVE RESPONSE:
SLAVE ADDRESS
FUNCTION CODE
BYTE COUNT
BIT MASK
6
CRC
Example 2: Request slave 11 to respond with status of digital inputs 1 to 4:
Digital Input
D1: Access
D2: Test
D3: Starter Status
D4: Emergency Restart
D5: Remote Reset
MASTER TRANSMISSION:
SLAVE ADDRESS
FUNCTION CODE
STARTING DIGITAL INPUT
NUMBER OF DIGITAL INPUTS
CRC
SLAVE RESPONSE:
SLAVE ADDRESS
FUNCTION CODE
BYTE COUNT
BIT MASK
CRC
6-4
Courtesy of NationalSwitchgear.com
Status Digital Input
Closed D7: Assignable Input 2
Open D8: Assignable Input 3
Open D9: Assignable Input 4
Open Bit Mask (LSB)
Closed Bit Mask (MSB)
Closed
BYTES
1
1
2
2
2
BYTES
1
1
1
2
2
Status Digital Input
Closed D6: Assignable Input 1
Open D7: Assignable Input 2
Open D8: Assignable Input 3
Open D9: Assignable Input 4
Closed Bit Mask (LSB)
BYTES
1
1
2
2
2
BYTES
1
1
1
2
2
469 Motor Management Relay
Status
Closed
Closed
Closed
0111 0001
0000 0001
EXAMPLE / DESCRIPTION
0B message for slave 11
02 read digital input status
00 05 starting at digital input 5
00 05 5 digital inputs (i.e. D5, D6, D7, D8, D9)
A8 A2 CRC calculated by the master
EXAMPLE / DESCRIPTION
0B response message from slave 11
02 read relay coil status
02 2 byte bit mask
71 01 bit mask of requested digital input
C5 B9 CRC calculated by the slave
Status
Closed
Closed
Open
Closed
0111 0001
EXAMPLE / DESCRIPTION
0B message for slave 11
02 read digital input status
00 01 starting at digital input 1
00 04 4 digital inputs (i.e. D1, D2, D3, D4)
28 A3 CRC calculated by the master
EXAMPLE / DESCRIPTION
0B response message from slave 11
02 read relay coil status
01 2 byte bit mask
01 bit mask of requested digital input
63 90 CRC calculated by the slave
6 COMMUNICATIONS
GE Multilin