Apple II no video display

Brent Hilpert bhilpert at
Fri Oct 27 15:13:01 CDT 2017

On 2017-Oct-27, at 12:13 PM, Ethan Dicks via cctalk wrote:
> On Fri, Oct 27, 2017 at 11:40 AM, Dave Wade via cctalk
>> The odd thing is that ic A9 appears to be a 74S151 not a 74LS151. I
>> wouldn't expect this to work, but I assume it was working at some point in
>> time!
> I don't think that should be a problem.  74S is often a sub for 74LS
> when the higher speed of 74LS is not required

74S is faster than 74LS, 74LS was combining low power techniques (which result in loss of speed) with Schottky technology to get some of the lost speed back, to get a better speed-power product than 'normal' TTL.

The chronological order of development was 74 --> 74H & L --> 74S --> 74LS

> but the higher drive of
> 74S is (and the higher power consumption of 74S is irrelevant
> in-circuit).  There are many times when you can put a 74S where it
> calls for a 74LS but often you can't sub 74LS for 74S where it's there
> intentionally.
> -ethan

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