Siemens SIMPRO-100 - Modbus Function Codes: Register Reads; 03 h Read Holding Registers Command; 04 h Read Input Registers Command

C
Modbus
™
RTU Communications Protocol
SIMPRO-100
160 PRIM-2400C
C.2.3 Supported Modbus
Function Codes
The SIMPRO-100 Relay supports the Modbus
function codes shown in Table C.2.
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.
Table C.3 Modbus Exception Codes
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.
Code Description
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
10h
a
Preset Multiple Registers
a
The
SIMPRO-100
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.
Exception
Code
Error
Type
Description
1
Illegal
Function
Code
The received function code is
either undefined or unsupported.
2
Illegal Data
Address
The received command contains
a unsupported address in the data
field.
3
Illegal Data
Value
The received command contains
a value that is out of range.
4
Device
Error
The SIMPRO-100 Relay is in the
wrong state for the requested
function.
6
Busy The SIMPRO-100 Relay is unable
to process the command at this
time due to a busy resource.
8
Memory
Error
There is a checksum error on the
stored data.