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lisp cards question

Posted by: chelseayr on 2023-06-09 13:30:00

just had to wonder what kind of processor these ran? (and I assume they're lga style too since it looks like one card had the original processor removed in favour of an upgrade daughtercard that has a bga variation mounted offside instead)

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and if noone minds a small offquestion - whats with these very long red component (if it can be called that)?

p.s I asked about the processor because it seem the weitek fpu is numbered 3164 and wikipedia seem to suggest that 31xx was perhaps for sparc but I can't be 100% sure about that tho ofc

Posted by: Nixontheknight on 2023-06-09 14:23:14

pretty sure that long red component is just the heatsink

Posted by: Phipli on 2023-06-09 15:21:36

pretty sure that long red component is just the heatsink

Nah, I have an 80s board with something similar, they're like buses for the RAM or something. Don't have a photo to hand.

@GRudolf94 would be able to tell you.

Posted by: GRudolf94 on 2023-06-09 19:46:18

These ran a custom, proprietary CPU (in PGA package, btw) called... Ivory. What says on the tin. Shame they tend to die on their own. The Weitek chip is just the FPA - they're fairly generic and can be interfaced to many things, or used standalone as part of a GPU, etc. The SPARC FPU is a part number distinct from this one. Red bars on the RAM expansion are decoupling.

Posted by: kkritsilas on 2023-06-09 21:06:25

The red strips are indeed power bus bars. Specifically, they are for VCC and Ground, and are also low value bypass capacitors of a sort. Internally, there are two buss bars (at least this is the form we used them in on our boards), one connected to VCC (usually +5V) and the other to Ground. You can think of the buss bars as the two plates of a capacitor. The buss bars have a much lower resistance than the equivalent track on a PCB. There is also some dielectric material between the two buss bars that helps create some amount (usually, not that high) of capacitance, so not only do they serve as buss bars, but they also remove the need for bypass capacitors. I think they were used until the mid/late 1980s, by which time surface mounted components had started to be used, and these disappeared. The buss bars have a lot of pins on them, and they are interleaved (one VCC, one ground, one VCC, one Ground, repeat as necessary for the full length of the buss bar. The buss bars simplified board layout, and increased board density in the memory section.

Posted by: cheesestraws on 2023-06-10 03:47:59

Rogers still make combination bus bars and decoupling caps. I can’t imagine they’re a very high volume product these days.

Posted by: chelseayr on 2023-06-10 04:38:35

thanks @GRudolf94 interesting history and i'm not too surprised that it would actually be a custom cpu given the particular history of lisp computers themselves

and I don't think I have seen or heard of these older kind of decoupling bars till I saw this particular card now, I'm not exactly an electrionics geek naturally

Posted by: kkritsilas on 2023-06-14 20:36:41

The buss bars/decoupling capacitor parts that we used were yellow coloured, probably because they weren't made by Rogers. They were coloured a mustard yellow, the colour being similar to what you would see on a tantalum bead (through hole) or surface mount capacitor. Ours looked more like they were conformally coated, which probably means that they were ceramic, and they were fired (melting the powder inside and outside the part) as part of the manufacturing process.