Modbus Master - Functionality - YASKAWA CP 341 Manual

VIPA System 300S

6.4.3 Modbus Master - Functionality

Overview
Message structure
ADDR
FUNC
Modbus Function codes
FC Function
01 Read coil status
02 Read input status
03 Read holding registers
04 Read input registers
05 Force single coil
06 Preset single register
07 Read exception status
08 Loop back test
11 Fetch communication event counter
12 Fetch communication event log
15 Force multiple coils
16 Preset multiple registers
HB130 | CP | 341-1CH01 | en | 18-40
With Modbus the data transfer happens without any handshake. The master initiates the
transmission, and after sending a request message it waits for a reply message from the
slave for the duration of the reply monitoring time set. The type of data transfer between
Modbus systems is controlled by function codes. The length of the message depends on
the used function code.
For communication Modbus uses the following message structure:
ADDR FUNC
Byte Byte
Modbus slave address with the range 1...255. With slave address 0 (Broadcast Message)
every slave at the bus is addressed by the master. This is only permitted in conjunction
with the writing function codes. Here the message is not applied by the slave.
The function code defines the meaning as well as the structure of a message.
The following function codes are supported by the driver:
DATA
n Byte
Action in the PLC
read in bits
read in bits
read in bits (16bit grid)
read in bits (16bit grid)
read in bits
read in bits
read in words
read in words
write in bits
write in bits
write in words
read in bits
-
read status word and event counter
read additional status
write in bits (1...2040bits)
write in bits (1...2040bits)
write in words (1...127 Register)
Communication protocols
Modbus > Modbus Master - Functionality
CRC-CHECK
Word
memory bits M
outputs Q
timer T
counter C
memory bits M
inputs I
data block DB
data block DB
memory bits M
outputs Q
event
-
status, event
status, event, mes-
sage
memory bits M
outputs Q
data block DB
55