7402 vs. 74L02 vs 74LS02 for Altair Clone

Can someone explain the main differences between those 3 families of logic chips?

I read "standard TTL inputs are stable floating, will read high" and that "you can't substitute modern TTL families for standard and expect some old equipment to work"

A project I am working on right now is duplicating an Altair 4k DRAM board. I'm preparing to place an order for the ICs. The manual calls for 74L02, 74LS00, and a 7406 (for examples). Did they choose these different styles (L vs. LS vs. 'nothing') because of cost or were they really necessary?

The manual (link included below) is GREAT. I wish all manuals could be this great. :) Not really...

For example Rev.0 of the board had a IC A, B, R as 74L04s and Rev2 changes B to an LS04. Rev0 has a 7420 for J and rev2 has an L20. Revo has a 7400 for L and K, rev2 has a 74LS for L and a 74L00 for K.

I suppose this could be due to wiring...

Do I really need to be this specific when ordering new logic chips?

I'm wondering if I need to special order these parts or if some of them will interchange. Will an LS part work in place of an L, or L in place of a 'nothing': LS work in the place of a nothing? Do you have any suggestions on how I could find information on these old parts? Searching in google only results in old stock results.

Here are 300dpi scans of the board and a datasheet in case you are interested.

If you're interested in my Altair duplication project send me an e-mail and I'll keep you updated.

1975 4k DRAM kit: Top Assembled - Top Bare - Bottom Bare - Manual -

Can someone explain the main differences between those 3 families of logic chips?

I read "standard TTL inputs are stable floating, will read high" and that "you can't substitute modern TTL families for standard and expect some old equipment to work"

A project I am working on right now is duplicating an Altair 4k DRAM board. I'm preparing to place an order for the ICs. The manual calls for 74L02, 74LS00, and a 7406 (for examples). Did they choose these different styles (L vs. LS vs. 'nothing') because of cost or were they really necessary?

The manual (link included below) is GREAT. I wish all manuals could be this great. :) Not really...

For example Rev.0 of the board had a IC A, B, R as 74L04s and Rev2 changes B to an LS04. Rev0 has a 7420 for J and rev2 has an L20. Revo has a 7400 for L and K, rev2 has a 74LS for L and a 74L00 for K.

I suppose this could be due to wiring...

Do I really need to be this specific when ordering new logic chips?

I'm wondering if I need to special order these parts or if some of them will interchange. Will an LS part work in place of an L, or L in place of a 'nothing': LS work in the place of a nothing? Do you have any suggestions on how I could find information on these old parts? Searching in google only results in old stock results.

Here are 300dpi scans of the board and a datasheet in case you are interested.

If you're interested in my Altair duplication project send me an e-mail and I'll keep you updated.

1975 4k DRAM kit: Top Assembled - Top Bare - Bottom Bare - Manual -

74 was the original chip series. 74L was the low power series 74LS was the low power cmos series.

And thats without googling. ( but I may be wrong )

I would just use what was cheapest, but trying to get the LS if possible because of the lower power usage.

74lsxxx is low power scottky (no cmos!!!!)

The 74 series is original TTL, power hungry, not so fast.

74L is a low power version, not not as fast, but with low power consumption and low input drive requirements (low fan in), but also low output current capability (low fan out).

74LS is a faster form of the low power TTL that raises the input current a bit, increases the output drive current considerable, compared to the L series and also increases the speed to faster than the original 74 series. The best performance to supply power ratio of the three.

Without reverse engineering the schematic, I can't say why the particular examples were chosen, but I doubt price was the issue.

Today, you have lots more choices, including the 74HCT cmos family, though its inputs cannot be left floating.

^^^^

Low Power Schottky.

74S is the Schottky series, very fast, but very high power consumption. 74LS melded the "L" series with the "S" series, and came up with low power, but fast, chips - mostly they replaced standard TTL (the 'nothing' series), because they worked at the same speeds at dramatically less power.

74C is the CMOS series, relatively slow, but almost no power consumption,

74HC is the high-speed CMOS series, really low power consumption at idle, but with mongo output drivers, ("High-Power CMOS", if that's not an oxymoron.[1])

74HCT is the high-speed CMOS series with TTL-compatible inputs. (HC outputs are practically rail-to-rail, so there's no problem with them driving practically anything, except maybe ECL, but that's a whole nother ball game...)

Oh, yes, Not googling is always wrong. Shame on you. >:-[ - ;-)

Or if you want to drag yourself kicking and screaming into the 21st century, you could look into HCT or even ACT. ;-P

Cheers! Rich [1] I have no idea where that word came from, and frankly, it sounds like pimple cream for retarded people. ;-P

NOOOOOOOOOOOOOOOOOO. DON'T GO THERE.

That board was a notorious piece of crap.

Nobody I knew who got one did anything besides mount it on their wall as a reminder to avoid repeating doing something as stupid as buying it and wasting their time trying to get it to work. After they replaced it with a nice 8K static RAM card.

If you're looking for something cool to duplicate, try the Cromemco Dazzler(?) color video display board set.

Mark Zenier snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)

Hello from the Constant Timelord No. 74LS was the Lowpower Schottky version of the SN74 series of devices. You are thinking of 74C which both TI and NSC made.

- Gregg drwho8 atsign att dot net "This signature is always right."

Is that why all of mine have been gutted of their parts?

The manual is sure pretty scary. This is Rev.2 and there are incorrect labels on jumpers all over the place.

Is this 4k DRAM board decent? It doesn't look like a kit model.

If all he wants is a cool project, he should build a TV typewriter from scratch. ;-) (Admittedly, when I built mine, I had access to an EPROM programmer and an almost infinite supply of chips. But pipelining the character EPROM so it could operate at sane speeds was way kewl!)

Cheers! Rich

Wow, it's been a long time since I've seen a MITS Altair memory board. I sort of remember that MITS had a _lot_ of problems with their early DRAM boards. I don't know if the board in the photo is one of the flakey boards. SRAM is a lot easier to work with than DRAM. I bought SRAM boards for my IMSAI (Altair clone) and never had memory problems.

-Dave Pollum