User`s manual

77
FX3U Series Programmable Controllers
User’s Manual - MODBUS Serial Communication Edition
7 MODBUS Standard Commands
7.18 Read/Write Multiple Registers (Command Code: 0x17)
1
Outline
2
Specifications
3
System Configuration
4
Wiring
5
Communication Setup
6
Related Devices and Comm. Status
7
MODBUS Standard Commands
8
Master Specification
9
Slave Specification
10
Creating Programs
7.18 Read/Write Multiple Registers (Command Code: 0x17)
Reads from and writes to multiple holding registers.
Writing is executed first and reading is then executed.
1) Request message format (Master → Slave)
*1. The number of the specified write points must be matched with the number of bytes.
2) Response message format (Slave → Master)
(When completed normally)
(When completed with an error)
*2. Exception and error codes are stored in special data registers and special auxiliary relays in the case
of error completion. Refer to Chapter 6 for storage location, confirmation methods, and other detailed
contents.
Data
(L) (L) (L)
. . .
(L) (L)(L)
Function
code
Function
code
(17
H)
Read head holding
register number
(0000
H to FFFFH)
Read points
n
(0001
H to 007DH)
Write head holding
register number
(0000
H to FFFFH)
Write points
m
*1
(0001
H to 0079H)
Number of
bytes
m x 2
*1
(0002
H
to 00F2 H)
(Number of bytes m x 2)
Write
device data
1
Write
device data
m
(H)
(H)
(H)
(H)
(H) (H)
Data
(L)
. . .
Function code
Function
code
(17
H)
Number of
bytes
n x 2
Read
device data
1
Read
device data
n
(Number of bytes n x 2)
(L)
(H)
(H)
Data
Function code
Function code
(97
H)
Exception
code *
2