User`s manual

FX3U Series Programmable Controllers

User’s Manual - MODBUS Serial Communication Edition

7 MODBUS Standard Commands

7.11 Diagnostics (Command Code: 0x08)

7.11.6 Clear counters and diagnostic register (sub-command code: 0x0A)

Clears counters (e.g. message count).

The following counters will be cleared. (Refer to Chapter 6)

• Bus message count

• Bus communication error count

• Exception error count

• Slave message count

• Slave no-response count

• Slave NAK count

• Slave busy count

• Character overrun error count

• Communications event count (Refer to Section 7.12)

The FX

3U bit devices displayed in the diagnostic register are not reset, so the diagnostic register will be

overwritten in the next scan by the actual state of the error flags. The error flags can be reset by PLC program

or monitoring device.

1) Request message format (Master → Slave)

2) Response message format (Slave→ Master)

(When completed normally)

The slave returns the request message received from the master without change.

(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.

(L)

Data

(L)

Function code

Function

code

(08

Sub-function code

(000A

(0000

(H) (H)

Data

Function code

Function

code

(88

Exception

code*