Re:Released the schematics and PCB of my transputer ISA board
by kragen on Sunday July 06, 2025 @03:55PM
(#44483533)
Oh! I usually think of availability as an advantage for 74HC (maybe not 74HCT) over 74LS, but maybe that's not the case where you are. Local availability is a real advantage.
The electronics parts stores in my town (Morón), which are several blocks from my house, have a fairly limited part selection, mostly for repair purposes. So part availability is a very significant concern. I was shocked to find last month that one of them didn't even have a TL431! But another one on the same block did.
I thought I'd check Digi-Key, but it seems like 74AS244 is even more than US$4 there in onesies: https://www.digikey.com/en/products/detail/texas-instruments... but a 74AHC244 is only 27¢: https://www.digikey.com/en/products/detail/texas-instruments... Thank you for explaining!
You cannot choose the source, these come mixed from ST, TI, and other manufacturers. I preferred the laser-engraved ones instead of the white ink ones just to have an uniform look.
The crystal oscillator needs something faster so it requires 74F04, and the link communication buffer requires 74F244 or 74AS244. These are more expensive, the 74F are 2 dollars each chip, and the 74AS are 4 dollars each chip.