RE: Another dumb EE question

> Why not use a 74LS138. It's an address decoder in one chip.
> The output is used as the CLK for the 74LS374 latch.
> Connect as follows: 74LS138

Hey, this is a great idea! I have a buttload of 74LS138s (literally about
a thousand) but no 74LS00s! And what's cool about this is later if I
decide to put in more write only peripherals, it'd be easy to do.
Splendid. Thanks for the suggestion!

> Connect the 74LS374 as follows:

Got tons of these, too.

> I hope this is what you wanted. I would like to make a small suggestion.
> Use a 74LS273 instead of a 74LS374. The LS273 replaces the OE/ with a
> Reset/ (active low) pin. This is VERY handy when using the latch for bank
> switching. Connect pin 1 of the LS273 to the master reset/ of the board
> and the output of the LS273 is guaranteed to be all zeros when the system
> resets. BTW the rest of the LS723 pin out is exactly the same as the LS374

I'm out of 273s. However, I don't think it's a big deal, because I'm only
bank switching vector ROMs - not code ROMs. The code EPROM just takes up
64K for now, and in the future if I want to bank switch 64K regions in and
out, I'll just make sure the bank switch code is "bank switch friendly".

Thanks for the suggestion! I'll take the 74138 and use it instead. I also
need an inverter for chip enable in the vector EPROM region (!VMEM), and I
have one unused NAND gate in the 7400 I installed last night. I just gotta
run the wires from the top of the board to the chip and back again. ;-(
Fortunately this is low speed logic so I can get away with that...

-->Neil

-------------------------------------------------------------------------------
Neil Bradley Play a song wrong once and it's a mistake.
Synthcom Systems, Inc. Play a song wrong twice and it's Jazz.
ICQ #29402898

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Received on Thu Apr 26 03:32:30 2001