These are all 74LSXX parts, nothing fancy, I need to use the old IC's
since Im replicating an existing 1983 circuit and want the same designed
prop delays etc. So... no HC stuff. :-)
Some of the pins I have tied high are the LOAD line on 74LS163 Binary
Loadable Counters, the CARRY IN pins on adders, etc.
The circuit Im replicating used a common 1K pullup resistor on all of
these so the hardware guru's at Atari must have had some reasoning... Im
just not quite sure that that reason was.
Frank Palazzolo wrote:
>
> Jess,
>
> I can't imagine an application where it would make much difference,
> especially with pull-ups. If they were pull-downs, then you might
> need slightly more power without resistors - at least with vanilla
> TTL. With CMOS, it makes no difference. Which exact logic family are
> you using? (I assume it's not "original TTL")
>
> Thanks,
> -Frank
>
> Jess Askey wrote:
>> can anyone explain what any pro's or con's there might be on tying
>> static input pins on a TTL device 'high' through a pull-up resistor
>> vs straight to the +5V supply? Im working on laying out a ASIC
>> replacement PCB and I had the board designed with pull-up resistors
>> but tracing them is becoming a PITA so I thought about just tying
>> them to the +5V rail as an alternative.
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Received on Wed Sep 6 23:39:31 2006
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