Mitsubishi Electronics FX3G Manuale Utente

240

/FX

3GC

/FX

3UC

Series

Programming Manual - Basic & Applied Instruction Edition

8 Program Flow – FNC 00 to FNC 09

8.8 FNC 07 – WDT / Watchdog Timer Refresh

2. The watchdog timer time can be changed.

→ For details on changing watchdog timer time, refer to Subsection 37.2.2.

By overwriting the contents of D8000 (watchdog timer time), the watchdog timer detection time (initial value: 200 ms)
can be changed.
By inputting the program shown below, the sequence program after this insertion is monitored by a new watchdog
timer time.

Program examples

1. When the operation cycle is long and causes an error

For example, by dividing a program whose operation cycle is 240 ms into two portions and inserting WDT instruction
between them, the operation cycle becomes less than 200 ms in both the former half portion and the latter half portion.

2. When a label (P) of CJ instruction is located in a step number smaller than the step number of CJ

instruction

Put WDT instruction after the label (P).

If an input relay (X) is used as the command
contact, input refresh is disabled, so the
program execution cannot be returned from
the area between P and CJ.
As the command contact, use such device
that can be set to OFF in a program being
jumped.

3. When FOR/NEXT instruction is repeated many times

Put WDT instruction between FOR and NEXT instructions.

M8002

Initial pulse

FNC 12

MOV

K300

D8000

FNC 07

WDT

Watchdog timer time: 300 ms

Watchdog timer refresh

If WDT (FNC 07) instruction is not programmed, the value of

D8000 is valid during END processing.

FNC 07

WDT

END

Program

whose

operation cycle

is 240 ms

END

Program whose

operation cycle

is 120 ms

Program whose

operation cycle

is 120 ms

M8000

RUN monitor

FNC 07

WDT

Label

Command

Program

FNC 00

When the command

contact turns ON

FNC 08

FOR

Program

FNC 07

WDT

K30000

FNC 09