Re: high level on different 6502

From: Francesco Messineo <>
Date: Sat, 5 Nov 2016 21:50:07 +0100
Message-ID: <>
On Sat, Nov 5, 2016 at 9:37 PM, didier derny <> wrote:
> while checking some signals on the 6502 of my 8032 motherboard
> I found the 'high' level rather low 2.5v  (I expected around 4v...)
> so I took my SYM1 board and tested several 6502
> MOS         6502       around  4v
> Rockwell  6502       around  4v
> Rockwell  65c02     around  5v
> Synertek  6502       around  2.5v
>                  CM630   around  4v      (bulgarian clone)
> I tried several 6502 of each type...

2.5V is really a bit outside the acceptable output High level for TTL logic.
2.7V is the official minimum level for the High state. However, TTL
inputs should accept as High any voltage => 2V.
If the current capability of the outputs isn't degraded (i.e. if 2.5V
is maintained at all the inputs when loaded at the max fan-out), I'd
say it should still work.
CMOS outputs, on the other hand, should go to the power rails, if they
aren't broken.
Do you have many Synertek and they all have the same output levels?


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Received on 2016-11-05 21:00:30

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