Replacement for a DEC 7474 Chip
rick at rickmurphy.net
Mon May 16 11:27:30 CDT 2022
On 5/15/2022 4:16 AM, Eric Smith via cctalk wrote:
> On Sat, May 14, 2022, 16:09 ben via cctalk <cctalk at classiccmp.org> wrote:
>> On 2022-05-14 11:50 a.m., Nigel Johnson Ham via cctalk wrote:
>>> AFAIR LS can only drive one unit TTL load.
>> LS is 4 TTL, 4 ma low.
>> Was there a trick of forcing the output of D flip flip
>> to clear it? I was wondering if this is what kills all
>> the 7474's?
> I don't think that worked on any TTL (or CMOS) 74x74 flip flops, except
> maybe by accident if you shorted the output enough to draw Vcc down (or
> ground up) enough to disrupt the FF, and then you have other problems.
> Despite the logic diagram showing feedback from the outputs, all 74x74 have
> buffered outputs. The recent TI data sheets show an equivalent schematic
> only for the 74LS74. I can't at the moment find one for the 7474.
> It seems likely to me that early pre-TTL logic families like RTL might have
> had FFs with unbuffered outputs, but I haven't checked.
I have several 7474s, including one marked DEC 7474. Sadly, I fear that
shipping from the US is likely to be prohibitive.
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