Re: Replacement for a DEC 7474 Chip

[Paul Koning via cctalk]

> On May 16, 2022, at 4:59 PM, Rob Jarratt via cctalk <cctalk@classiccmp.org> 
> wrote:
> 
>> 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?

I can think of two ways to answer that: (1) ask and see if you get an answer, 
hopefullly a correct one, (2) find the data sheet for the 74x74  you're looking 
at, and the devices it is driving, and do the calculation.  Sum up the max 
input currents of the driven devices, compare with the min output current of 
the 74x74.  If the output current is >= the load current, you have the needed 
fanout.

        paul