In article , "Ernest" wrote: > Does anyone know of a book or website that describes what each of the > different ICs (74LS* chips) on the Apple II and clone motherboards do? I'm > going to be starting a "compare and contrast" project between the Apple II+ > and my different clone motherboards, which often have some interesting > differences. If I can figure out what each of the different chips are for, > then I might be able to better understand why chips were added or removed on > different boards. That's my hope anyway. 7400-series chips are "commodity" logic chips. Depending on the number on it, it might be an "OR" gate, a "NAND" gate, or any of several steps of complexity, all the way up to a complete subsystem such as a one-chip stepper-motor driver or mux/demux. Punch any one of them that you're interested in into google, adding a space, and the magic incantation "+datasheet" after the numbers. Don't give up if the first try gets you nothing - If you've got, for instance, a chip labeled 74HCT123N, try it first exactly as-labeled. If that returns no hits, try it as 74HCT123. If that gets you nowhere, try it as 74LS123, and keep on trying until you've found a match - the letters in the middle are different specs for the same chip - an "LS" chip is built around the "Low-power Schottky" technology, the "HCT"s perform just a touch differently (electrically speaking - identical as far as logic operation and pinout are concerned) than their LS counterparts, which makes them useful for certain "trick" ways of getting a job done (An oscillator built out of a nor gate, two caps, two resistors, and a crystal, ferinstance - Because of electrical differences, the "LS" chip won't oscillate at all, but the "HCT" version will give you a gorgeous square-wave at the crystal's rated speed) and so on. The trailing letter (usually only one, but sometimes two letters) usually indicates package type and/or temperature range - Perhaps a "C" on a ceramic-case version of the chip, with a "P" on the plastic version, and similar. Once you've found the datasheet for the chip, you've got everything you'll ever need to know about it (and probably some extra that you didn't even know COULD be known!) On a related note: If you find you need substitutes for any reason, and you're having a hard time finding one - Or perhaps you encounter one on one of those clone boards - let's say you need a replacement 74LS323 - You can *USUALLY* change the "74" to "54", pay a little extra, and get yourself the military/hostile environment version of the chip - So for the '323 you need, you can probably find it as a 54LS323, and it will be pin-compatible with the 74LS323 version. Likewise, if you encounter a 54xxx chip, it's just the military/hostile environment version of the 74xxx. Note that the 74/54 crossover dosn't necessarily work well for the "tricky" stuff like the NOR-gate oscillator I mentioned above - For situations where you're using the chip purely as a logic gate/module, you should never see a problem. Start playing with "weird" stuff like the oscillator example, and you may very well find that what works perfectly with a 74xxx chip in the socket either doesn't do anything at all, or worse - but unlikely - "lets all the smoke leak out" when a 54xxx chip is put in its place. -- Don Bruder - dakidd@sonic.net - New Email policy in effect as of Feb. 21, 2004. Short form: I'm trashing EVERY E-mail that doesn't contain a password in the subject unless it comes from a "whitelisted" (pre-approved by me) address. See for full details. Ernest wrote: > Does anyone know of a book or website that describes what each of the > different ICs (74LS* chips) on the Apple II and clone motherboards do? I'm > going to be starting a "compare and contrast" project between the Apple II+ > and my different clone motherboards, which often have some interesting > differences. If I can figure out what each of the different chips are for, > then I might be able to better understand why chips were added or removed on > different boards. That's my hope anyway. > > Thanks. > > E. > http://www.apple2clones.com Another poster suggested googling for datasheets, and that's a good suggestion, will probably work. You might also find it useful to go directly to the site of one or more known manufacturers of 7400 chips, such as Texas Instruments. Either way, the PDF datasheets are the definitive word. However, the set of chips used in the Apple II was fairly small (and slightly idiosyncratic!); ISTM a discussion of them here might be of interest. The Apple II was one of the first (and last) computers that I felt I fully understood, at the chip level. It made a great learning platform for hardware engineering, as well as software. Glancing at the schematic, here's a few that I see, along with the partial info that I have: 74LS00 Quad NAND gate. 74LS02 Quad NOR gate. 74LS04 Hex inverter. 74LS08 Quad AND gate. 74LS11 Triple 3-input AND gate. 74LS20 Dual 4-input NAND gate. 74LS32 Quad OR gate. 74LS51 74LS74 Dual D flip flop. 74S86 Quad XOR gate. 74LS138 3-to-8 demultiplexer. 74LS139 Dual 2-to-4 demultiplexer. 74LS153 Dual 1-of-4 multiplexer. 74LS161 4-bit binary counter. 74166 8-bit parallel-load shift register. 74LS174 Hex D flip flop. 74S175 Quad D flip flop. 74LS194 4-bit universal shift register. 74S195 4-bit universal shift register. 74LS251 1-of-8 multiplexer. 74LS257 Quad 2-to-1 multiplexer. 74LS259 8-bit addressable latch. 74LS283 (555) Timer. (558) Quad timer. (741) Op amp. (2513) (HT28) (HT97) Add/correct at will... --Benjamin "Ernest" writes: > Does anyone know of a book or website that describes what each of the > different ICs (74LS* chips) on the Apple II and clone motherboards do? TTL Databook for Design Engineers, Second Edition, by Texas Instruments. Long since out of print, but you should be able to find a used copy. Alternatively, just go to http://www.ti.com/ and type the part numbers into the search box (one at a time). None of the 74xx TTL chips in the Apple II are very obscure. Probably the most difficult to find information on at this late date will be the DP8304 bus buffers used in some revisions, but they are very similar to the 74LS245. Also note that some 74xx chips have non-74xx equivalents. For instance, the 9334 and 74LS259 are interchangeable 8-bit addressable latches.