Replacement for a DEC 7474 Chip
robert.jarratt at ntlworld.com
Mon May 16 15:59:40 CDT 2022
> -----Original Message-----
> From: cctalk <cctalk-bounces at classiccmp.org> On Behalf Of Rick Murphy via
> Sent: 16 May 2022 17:28
> To: cctalk at classiccmp.org
> Subject: Re: Replacement for a DEC 7474 Chip
> 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.
> >>>> paul
> >> 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
> > 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.
I have ordered some 7474s. However I am getting a bit lost in the discussion now. From a simple fan out point of view, would an S be sufficient to replace it?
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