User`s manual

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FX3U Series Programmable Controllers

User’s Manual - MODBUS Serial Communication Edition

7 MODBUS Standard Commands

7.4 Read Coils (Command Code: 0x01)

Reads the status (ON/OFF) of one or more coils.

1) Request message format (Master → Slave)

2) Response message format (Slave → Master)

(When completed normally)

(When completed with an error)

*1. 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)

Function code

Function

code

(01

Head coil number

(0000

H to FFFFH)

Read points

(0001H to 07D0H)

(H)

Data

b0b1b2b3b4b5b6b7

Function code

Function

code

(01

Number of

read bytes

Device data

(Number of read bytes n)

(Device data 1 to n)

Device data 1

Device data n

Bit device

storage order

0 : OFF

1 : ON

The read coil statuses are stored in order from low-order to high-order bits.

When the number of read points is not a multiple of 8, the excess bits turn to 0.

Data

Function code

(81

Function code

Exception

code*