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Old 26th Apr 2018, 6:58 pm   #31
TonyDuell
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Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,191
Default Re: MK14 schematic revisions

I seem to remember that the 7408s are used as the anode drivers for the display. As such they are expected to source more current than the data sheet suggests, and you really do want the plain 7408 here.

The 7445 is the open-collector version of the 7442. Again it was chosen for a good reason, you do not want to be shorting totem-pole outputs together if you happen to press 2 keys at once.

The 80L95 is equivalent to one of the 74LS365/6/7/8 ICs (I forget which), so if the 74LS365 looks to be the same, it will work.

The latches for the display anode (segment) signals are 74LS157s. Yes, multplexers. The rumour at the time was that they should have been specified as 74LS175s (D type latches) but somebody ordered the wrong part and the design was modified to use them. My experience is that not all 74LS157s work, you may need to select some.
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