Modbus Functions; Supported Functions; Function Codes 01/02: Read Relay Coil / Digital Input Status - GE 469 Instruction Manual

6 COMMUNICATIONS

6.2MODBUS FUNCTIONS

The following functions are supported by the 469:
Modbus Function Code 01: Read Relay Coil
Modbus Function Code 02: Read Digital Input Status
Modbus Function Code 03: Read Setpoints and Actual Values
Modbus Function Code 04: Read Setpoints and Actual Values
Modbus Function Code 05: Execute Operation
Modbus Function Code 06: Store Single Setpoint
Modbus Function Code 07: Read Device Status
Modbus Function Code 08: Loopback Test
Modbus Function Code 16: Store Multiple Setpoints
Modbus implementation: Read Coil and Input Status
469 Implementation: Read Relay Coil and Digital Input Status
For the 469 implementation of Modbus, these commands can be used to read Relay Coil Status or Digital Input Status.
MESSAGE FORMAT AND EXAMPLE, FUNCTION 01:
The standard implementation requires the following: slave address (one byte), function code (one byte), starting relay coil
(two bytes), number of coils to read (two bytes), and CRC (two bytes). The slave response is the slave address (one byte),
function code (one byte), relay coil mask byte count (one byte; always 01 since only six relay coils), bit mask indicating the
status of requested relay coils (one byte), and CRC (two bytes).
Request slave 11 to respond with status of relay coil 3 to 5:
Relay Status
R1 Energized
R2 De-energized
R3 De-energized
R4 De-energized
R5 Energized
R6 Energized
Bit Mask 0011 0001 (0 x 31)
MASTER TRANSMISSION:
SLAVE ADDRESS
FUNCTION CODE
STARTING RELAY COIL
NUMBER OF RELYAS
CRC
SLAVE RESPONSE:
SLAVE ADDRESS
FUNCTION CODE
BYTE COUNT
BIT MASK
CRC
If a Starting Relay Coil (Starting Digital Input) of Zero is entered, the 469 will default it to One. If the Number of
Relays (Number of Digital Inputs) requested exceeds the number of relays available, the user is prompted with a
NOTE
message.
ILLEGAL DATA
GE Multilin
Courtesy of NationalSwitchgear.com

6.2.2 FUNCTION CODES 01/02: READ RELAY COIL / DIGITAL INPUT STATUS

BYTES EXAMPLE / DESCRIPTION
1 0B
1 01 read relay coil status
2 00 03
2 00 03
2 8C A1
BYTES EXAMPLE / DESCRIPTION
1 0B
1 01 read relay coil status
1 01
1 10
2 53 93
469 Motor Management Relay
6.2 MODBUS FUNCTIONS

6.2.1 SUPPORTED FUNCTIONS

message for slave 11
starting relay coil 3
3 relays coils (i.e. R3, R4, R5)
CRC calculated by the master
response message from slave 11
1 byte bit mask
bit mask of requested relay (0001 0000)
CRC calculated by the slave
6
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