At 11:05 02-02-22 +0200, you wrote:
>The NMOS (n-channel metal oxide semiconductor) chips in the Commodore can
>actively pull signals down, but not up. The opposite is PMOS, which is
>quite rare, I think. The combination of NMOS and PMOS is called CMOS
>(complementary metal oxide semiconductor), which can drive signals both up
>and down. [...]
>
>I also noticed that the 33pF capacitors in the crystal circuit are
>unnecessary. (How did I find this out? I have run out of SMD caps and
>resistors; I only had the five capacitors for the MAX232.)
>
> Marko
To make it clear: NMOS technology use two kinds of N-channel transistors:
enhancement mode (normally off) and depletion mode ones (normally on). CMOS
technology use enhancement mode N-channel and P-channel (instead of
depletion mode N-channel).
I haven't heard of PMOS logic chips - but the hole mobility is about 2.5
times less than electron mobility and P-channel transistor should have ~2.5
times wider channel to have the same transconductance as N-channel one. So
PMOS gates would simply be bigger...
Marko - have you tried to exchange the crystal with a different one ? I'm
curious if it's not just an accident, that oscillator runs without
capacitors. Once I was doing something with AT-mega, and it didn't work
without capacitors. Also didn't work with 100nF one (a guy put one 33pF and
one 100nF by a mistake) ;-)
Konrad Burylo
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