Siemens SIRIUS 3RW5 Equipment Manual page 100

Messages and diagnostics
7.2 Function Codes
7.2.1 Function Codes 01 (Read Coils) and 02 (Read Discrete Inputs)
These functions enable the reading of individual bits from the 3RW5 bit memory area by the
Modbus TCP client system or the Modbus RTU master system.
Function Codes 01 and 02 behave in the same way here and supply an identical feedback
signal. A valid offset from the bit memory area is expected as the start address. Up to
2 000 bits can be read per telegram.
If a number that is not equal to a multiple of 8 bits is called up, the remaining bits are filled
with zeros. The number of bytes n always refers to the number of fully returned bytes.
Note
Start address and number of Coils
The start address and the number of coils must be within the valid range.
Request telegram
Modbus TCP:
Address Field
7 bytes
-
Modbus RTU:
Slave address
1 byte
-
Response telegram
Modbus TCP:
Address Field
7 bytes
-
Modbus RTU:
Slave address
1 byte
-
100
Function Code
1 byte
0x01
Function Code Start address
1 byte 2 bytes
0x01 0x84EF
Function Code
1 byte
0x01
Function Code Number of bytes n Bit status
1 byte 1 byte
0x01 0x01
Start address
2 bytes
0x84EF
Number of bits
2 bytes
0x0001
Number of bytes n
1 byte
0x01
n bytes
0x01
SIRIUS 3RW5 Modbus communication module
Equipment Manual, 03/2020, A5E43676481002A/RS-AC/003
Number of bits
2 bytes
0x0001
CRC
2 bytes
-
Bit status
n bytes
0x01
CRC
2 bytes
-