Siemens SIMOCODE pro Function Manual page 106

Communication
2.3 Modbus communication
Function code 23 - Read/Write Multiple Registers
Function
This function enables the Modbus master system to write and read several registers from
SIMOCODE using a single function call. The write operation is the first executed operation
here. This function is the typically used function call for outputting cyclic data in SIMOCODE
and for reading back inputs or device statuses.
A valid address from the register memory area is expected as the start address. The
selected address must be designated as writable (see the tables in Section Modbus RTU
data tables (Page 277), "Access" column).
Request message frame
Slave
address
1 byte
Response message frame
Slave address
1 byte
Example
Writing the outputs and reading back the input signals of the SIMOCODE pro device. To do
this, register 0x0000 in the PIQ (process image output) is written, and at the same time,
4 registers from 0x0400 in the PII (process image input) are read. Slave address of the
SIMOCODE pro = 16 (10h).
The register written to SIMOCODE here is to start the motor in clockwise rotation
in "Remote" mode (24h).
In this example, it must be noted that the requested function "Start motor clockwise" is not
returned in the same cycle as the new status. This is due to the ON command execution
time in SIMOCODE and the delay of the contactors. Not until a few communication cycles
later will the feedback signal of the PII also begin with 0x0024.
Note
Read/Write Multiple Registers
The FC23 can only access the PII/PIQ.
106
Function Start Number of
code address registers
read (read
operation access)
1 byte 2 bytes 2 bytes
Function code
1 byte
Start Number
address of
write registers
operation N (write
access)
2 bytes 2 bytes
Number of Data
bytes N
1 byte Nx2 bytes
Function Manual, 11/2018, A5E40508495002A/RS-AC/003
Number Data CRC
of (write
bytes access)
(write
access)
1 byte Nx2bytes 2
bytes
CRC
2 bytes
SIMOCODE pro - Communication