childs@rodan.caltech.edu (01/24/89)
Hi everyone, I just finished building my Lucas Board this weekend. I am having a little trouble with it. On the replacable 7474 at U9, I am having the best luck with a 7474. I havn't got a 74ALS74 to try yet, but the 74S74 and the 74LS74 don't work most of the time. I really have to seat the board and the chips well to get it to work at all. I get a Green screen a lot of the time, which is suppost to mean bad RAM chip. When I hook up my Megaboard 2 and my SupraDrive it is even more difficult to get the machine to boot, but with time it will boot. I did the grounding fix while my machine was open. (You connect the PALS ground to the metal flange thing around the expansion connector, right?) The problem I get is doing a SupraMount after normal boot up finally works. Everytime the machine hangs doing a SupraMount. I am calling Supra when they open to see if they have any ideas. (A normal boot in this case is actually not having an s:startup-sequence so all I get is the blank cli. I usually do a Supramount first, and then run a startup-sequence off of my hard disk.) I have a 16Meg Clock on the lucas board, and will get a 20Meg part when I find one. The hardest parts to get were the sockets for the 68881, and 68020. BTW, how much will I gain by using a 68882 insted of the 68881? My wife found out that Leasure Suit Larry doesn't work with the 68020. Copy protection I guess. I built the board with the 'keep the 68000 mod' in mind, so I have a usable 68000 socket on the lucas board. I wanted to do something like this (drawing below) for the mod to keep things cleaner. ________ <-- 68000 in wire wrap socket on Lucas Board / \ --|--------|--------------------------------------------- <-- Lucas Board | ---- | -|-/----\-|- <-- Little perf board with 74244, resistors & capacitors on it. | | | | | | |--------| <-- Solder tail socket to solder wire wrap socket to. | | ... Any problem with this? I couldn't figure out a good place to put the extra stuff. Thanks, David
rokicki@polya.Stanford.EDU (Tomas G. Rokicki) (01/25/89)
> trouble with it. On the replacable 7474 at U9, I am having the best luck > with a 7474. I havn't got a 74ALS74 to try yet, but the 74S74 and the 74LS74 > don't work most of the time. Folks, these parts are *not* interchangeable, especially flip-flops! I don't have my databooks around, but for some the combinations a direct flip-flop to flip-flop won't work if they are of different families because of the setup and hold vs. delay times! Don't just switch parts around like this unless you have your TTL data book and a good timing diagram of the circuit you are messing with. You're just asking for intermittant failures. Conservative design, folks, conservative design.
anakin@gpu.utcs.toronto.edu (Anakin Research) (01/25/89)
David,
My buudy has done the 68000 mod in a similar way and it is working
fine for him. I might suggest you try and build a bus terminator{ alot of
folks out there are having great success with it, and the LUCAS Board.
E-mail me for details
Brad Fowles anakin@gpu.utcs.toronto.edu