Modbus Operation
X-600M Users Manual
5.3 Modbus Function Codes
The following sections describe the function codes supported by the X-600M
5.3.1 Read Coils - Modbus Function Code 01 (0x01)
Read the state of the relays that have been added to the Modbus coil table.
Request
Start Address: 0x0000 (coil 1) to 0x00FF (coil 256)
Coil Quantity: 0x0001 (1 coil) to 0x00FF (255 coils)
Multiple Outputs may be read at the same time by specifying the correct starting address and quantity of
coils to be read.
Response
The X-600M will respond to the request with a data field of one byte, each bit representing the coil
status. A '
1
' indicates the Output is
ON
. A '
0
' indicates that the Output is
OFF
.
Bit zero of the return value will be the state of the coil corresponding to the start address. For example, if
a start address of 0x0001 is used, bit zero will be the status of Relay 2 assuming Relay 2 is found in the
coil address table.
Coil State Byte
Bit 7
6
5
4
3
2
1
Bit 0
X
X
X
X
Relay 4
Relay 3
Relay 2
Relay 1
Errors
The sum of the start address and coil count cannot exceed the maximum coil count or an error response
will be returned.
The following are possible error responses:
Coil Read Error Function Code (1 byte): 0x81
Exception Codes (1 byte):
0x01 – Function code not supported.
0x02 – Incorrect combination of start address and quantity of Relays
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Xytronix Research & Design, Inc.
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