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Tracking Down a RAM Issue in a VT100 (how does the 2114 chip work?)

by Rob Jarratt

I have a non-functioning VT100. I think it is failing in the POST during the RAM check. I don't know for sure because I can't get it to light up the LEDs on the keyboard, however I used my logic analyser (a HP1630G) to see what values were written to the UART to send to the keyboard and I see it sends the values FF then 1, 2, 3, 4 and finally 5. The last value corresponds to the RAM test so I am fairly confident the RAM test is what is failing. I have disassembled the VT100 ROM and if I have understood it correctly it zeroes out the RAM (high address to low) and then for each address (low address to high) it tries first to read back the zero and then writes 0xAA to the location and tries to read that back. I am also confident the 8080 is working OK because I was able to capture an address trace on the ROM that showed it executing the program as per the disassembled ROM. My problem is getting the logic analyser reliably to tell me how each RAM chip is being addressed and what data is being read or written. I am seeing strange values for the addresses (sometimes) and I am not sure I have setup the logic analyser correctly. I have read the datasheet for the 2114 chip and I am not entirely clear that I have understood it correctly. Here is how I have set it up: Trigger on the -ve edge of Chip Select (pin 8) Capture A9-A0 as the address Capture WE as an indication of Read or Write The timing diagrams show the write cycle where the WE signal and CE signal seem to transition at the same time and the data may be only valid a bit later then the CS -ve edge. But this may just be me not knowing how to read the datasheet. Using the +ve edge of CS seems no better. Is there something I am missing about how to analyse how the RAM chips are being used? Thanks Rob

2 years, 2 months

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Concorde cabin display technology?

by Shoppa, Tim

Not quite computer tech but I figure this is the best place to ask: Does anyone recognize the display tech that was used on the Concorde's in-cabin display? Examples: https://samchui.com/wp-content/uploads/2016/02/CON15.jpg https://samchui.com/wp-content/uploads/2016/02/CON16.jpg The display had fully-formed digits and letters, and showed either Mach and Feet, or Temp and MPH. Some pictures show the display in green and others show it in orange - which of course were popular monochrome CRT colors, yet the display looks too "flat" to be a couple CRT's. Those colors were also popular for Electroluminiscent displays which matches the evident "flatness" but I'm not sure I've seen any EL's with fully formed digits like this with no visible segmentation? I want to guess it was individual digits back-projected - which was a popular control-theater display tech at the end of the 20th century - but I can't rule out, say, really well-done edge-lit character plates. In any event there doesn't seem to be any visible jitter up and down between digits that I might expect with either of those technologies. The "FEET" display in the above-referenced JPG's shows some artifacts at the left and right edges which might be a clue? Some pics of the BA Concorde interior had a simple 15-segment and 7-segment green LED display. Don't need help with that one 🙂. Tim N3QE

2 years, 2 months

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OT: Anyone near Glasnevin (Dublin), Ireland (to pick-up an item)?

by Sellam Abraham

I'm looking for someone near Glasnevin near Dublin, Ireland who would be willing to pick up an item for me and ship it to me State-side. Seller will not ship. Thank you in advance. Sellam

2 years, 2 months

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WTB: IBM 9221 ESCON card

by Kevin Bowling

Hi, I am looking for a CH3s QH50, P/N 63F3825 for a 9221 ES/9000. A CH1s would also do. Anyone have an ES/9000 that is a brick because no processor console that can help me out? Regards, Kevin

2 years, 2 months

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Re: Looking for an original Sun PS2 ->Sun keyboard adapter 370-2068

by silcreval

I've not heard of the Wombat adapter - was that Sun related?

2 years, 2 months

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Re: Looking for an original Sun PS2 ->Sun keyboard adapter 370-2068

by silcreval

Thanks - I did spot that - just hoping to get a slightly better price if I can :-)

2 years, 2 months

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Comparing PDP-8 processor flipchip

by Bill Degnan

The recent Ebay auction for the original PDP-8 got my attention because one of the photos (the processor logic flipchip array) is a nice snapshot for comparison purposes with the system I am working on. https://vintagecomputer.net/digital/pdp-8/PDP-8_flip-chips_left.png (mine) https://vintagecomputer.net/temp/EBAYPDP-8ProcessorFlipchips.jpg Given my PDP-8 is close to working, I would assume that the Ebay PDP-8 would have a fighting chance, at least as far as the flip chip configuration goes. This is also a nice confirmation that I more or less have the flipchips in the right places. There are only a few slight differences. Bill

2 years, 2 months

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Looking for an original Sun PS2 ->Sun keyboard adapter 370-2068

by Ian F

Hi all, Looking for an original Sun 370-2068, which is a PS2 to Sun keyboard adapter. If anyone has one please DM me, happy to pay a reasonable price & international shipping if needed. Thanks!

2 years, 2 months

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For Fred, especially: "Everything I know about floppy disks"

by Liam Proven

« Everything I know about floppy disks 2023-08-28 Floppy disk drives are curious things. We know them as the slots that ingest those small almost-square plastic "floppy disks" and we only really see them now in Computer Museums. But there's a lot going on in that humble square of plastic and I wanted to write down what I've learned so far. » https://thejpster.org.uk/blog/blog-2023-08-28/ -- Liam Proven - Profile: https://about.me/liamproven Email: lproven(a)cix.co.uk - Google Mail/Hangouts/Plus: lproven(a)gmail.com Twitter/Facebook/Flickr: lproven - Skype/LinkedIn: liamproven IoM: +44 7624 227612 ~ UK: +44 7939-087884 ČR (+ WhatsApp/Telegram/Signal): +420 702 829 053

2 years, 2 months

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Anyone in Sheffield uk?

by Ethan O'Toole

Anyone in Sheffield UK? There is an Acorn Archemedies computer I am interested in buying but the guy is collection only. I am in the USA, but interested in buying and repairing the system. - Ethan

2 years, 2 months

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