Siemens SIRIUS 3RW5 - Page 100

Messages and diagnostics
7.2 Function Codes
SIRIUS 3RW5 Modbus communication module
100 Equipment Manual, 03/2020, A5E43676481002A/RS-AC/003
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 mu
st be within the valid range.
Request telegram
Modbus TCP:
Address Field
Function Code
Start address
Number of bits
7 bytes
1 byte
2 bytes
2 bytes
-
0x01
0x84EF
0x0001
Modbus RTU:
Slave address
Function Code
Start address
Number of bits
CRC
1 byte
1 byte
2 bytes
2 bytes
2 bytes
-
0x01
0x84EF
0x0001
-
Response telegram
Modbus TCP:
Address Field
Function Code
Number of bytes n
Bit status
7 bytes
1 byte
1 byte
n bytes
-
0x01
0x01
0x01
Modbus RTU:
Slave address
Function Code
Number of bytes n
Bit status
CRC
1 byte
1 byte
1 byte
n bytes
2 bytes
-
0x01
0x01
0x01
-