Re: Two projects

From: John (
Date: 1998-03-24 19:48:23

>>  most signals (but I don't think ALL signals) go OUT though an
>>  inverter but they come IN without an inverter.

>NPN transistors behave better and quicker for some reasons then PNPs. It has 
>something to do with quantum mechanics I was told so don't ask me further :-)

Electron mobility in silicon is higher than hole mobility.  But that has
nothing to do with the 1541.  The serial bus uses open-collector drivers
for the outputs.  In the 1541, they use a 7406 (this is from memory - might
be wrong), which inverts the signals.  The lines are connected directly to
the inputs, so they're not inverted (there's probably a series resistor or
something to protect the PIAs, but the signal still doesn't get inverted).

Why do they use open collector drivers?  So you can connect more than one
device to the same wires.

John West

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