Michael Karas wrote:
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A far better scheme than trying to use the ALE signal would be to allocate a different ordinary port pin as an output. Put into your code someplace some logic that will output a narrow trigger pulse on this pin from time to time. (For example in main loop of program have the pulse go out every N times around the main loop where N is divided down by a software counter variable).

Dear Michael Karas,

What about if all i/o pins occupied for doing job,
and if there any addition signal at any pin
the job goes wrong.

I am considering of using your idea (such as 74ls121
or 74ls123) triggered by ALE or PSEN.

Thank you very much.
Kurnia Brahmana