Supported Modbus Function Codes; Modbus Exception Responses; Cyclical Redundancy Check - Siemens SIMPRO-100 Instruction Manual

C
™
Modbus RTU Communications Protocol
C.2.3 Supported Modbus
Function Codes
The SIMPRO-100 Relay supports the Modbus
function codes shown in Table C.2.
Code
01 Read Coil Status
02 Read Input Status
03 Read Holding Registers
04 Read Input Registers
05a Force Single Coil
06a Preset Single Register
07 Read Exception Status
08 Loopback Diagnostic Command
a
10h Preset Multiple Registers
a
SIMPRO-100
The Relay supports broadcast operation
for these function codes. Broadcast function codes use
slave device address 00h. Slave devices do not send a
response to broadcast functions.
Table C.2 Modbus Function Codes
C.2.4 Modbus Exception
Responses
The SIMPRO-100 Relay sends an exception
code under the conditions described in Table C.3.
Exception Error
Code Type
Illegal The received function code is
1 Function either undefined or unsupported.
Code
Illegal Data The received command contains
2 Address a unsupported address in the data
field.
Illegal Data The received command contains
3
Value a value that is out of range.
Device The SIMPRO-100 Relay is in the
4 Error wrong state for the requested
function.
Busy The SIMPRO-100 Relay is unable
6 to process the command at this
time due to a busy resource.
Memory There is a checksum error on the
8
Error stored data.
Table C.3 Modbus Exception Codes
160
Description
Description
In the event that any of the errors listed in
Table C.3 occur, the relay assembles a response
message that includes the Exception Code in the
Data field. The relay sets the Most Significant Bit
in the Function Code field to indicate to the
master that the data field contains an error code
rather than the requested data.
C.2.5 Cyclical Redundancy
Check
The SIMPRO-100 Relay calculates a 2-byte CRC
value using the device address, function code,
and data fields. It appends this value to the end of
every Modbus response sent. When the master
device receives the response, it uses the
received data to recalculate the CRC value using
the same CRC-16 algorithm. If the calculated
CRC value matches the CRC value sent by the
SIMPRO-100 Relay, the master device uses the
data received. If there is not a match, the check
fails and the message is ignored. The devices
use a similar process when the master sends
queries.
SIMPRO-100
PRIM-2400C