Re: 74HC123 and 74LS123

jhomppi
Date: 01/07/05 

Date: Fri, 07 Jan 2005 17:37:41 GMT

On Thu, 6 Jan 2005 13:56:19 -0600, "Martin" <Martin@123.com> wrote:

I am glad that you got it working.

In case you do future projects here is some more explanation
about pin 15 and pin 8 (not pin 0, sorry my eyes are bad).

Pin 15 supplies power to the chip. Similar to electricity supplied to
home appliances. Each applicance (ie chip) needs its own supply to
operate correctly regardless of the other connections.

Simple analogy for sci.electronics.basics:
Suppose I buy a new TV and a new stereo amplifier.
I connect the TV audio output to the stereo audio input.
I plug the TV into the wall outlet and turn it on and hit
the "on" switch of the stereo ..... no sound comes out of the stereo.
I forgot to plug the stereo into a wall outlet. Both the TV and the
stereo amplifier needs power to operate.

The schematic with the single 74HC123 has both the A and B circuits
powered from pin 15 of the single chip. If you use separate 74HC123
chips then you must provide power to each of the chips.
ie. Both 74HC123 chips must have their pin 15 attached to the +5V
power supply. (ditto for the ground on pin 8).

Be aware that sometimes (infrequently) schematics omit the power
supply pins and ground pins for chips assuming that readers of the
schematic know that chips need power.

>Well last night I re did things using one 74HC123 chip and grounded 14 and 6
>and it appeared to work.
>
>Im not sure what you mean by 15 and 0. on Chip B. Since on Chip A 15 is
>already used up So it cant be used again on B and I'm unfamiler with pin 0
>unless your talking SCSI language where 0 is the first device. But I dont
>think there is a pin 0, unless you mean pin 1? Which is again being used on
>Chip A.
>
>In either case I think it is working for me now. Thanks.
>
>

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