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ClausB

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About ClausB

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    River Patroller

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    Male
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    Michigan
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    space and rocket history, astronomy, photography, math, computer programming, physics, digital electronics, Atari, aviation, sports cars, Star Trek, Star Wars, Doctor Who, my family, to name a few

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  1. I built two ZX81 kits and met a lasting friend who had a ZX80. Thanks, Sir Clive!
  2. Thanks, that confirms it. If you want 256K, wire U20 pin 1 to ground and insert a 74LS153 into the socket at U20. BTW, this isn't an attempt to modify the 1066 into what it's not. Clearly the original designers had 256K in mind. They got most of the way there and then backed off for some reason. The date on the original schematic is May or June, 1984, months before I designed the 256K upgrade for the 800XL which appeared in BYTE a year later.
  3. It's hard to tell from the photos whether those are copper connections or just silk screen lines. Could someone post a close up photo of U20 and U21 on the bare board, maybe both sides?
  4. From the board photos it appears that U20 pin 1 goes to U21 pin 19. If so, that's fine and it doesn't need to go to ground. It also appears that U20 pins 1 and 16 are connected. That's bad. Pin 16 should connect to +5V, not to pin 1.
  5. I took the liberty of modding the schematic for 256K. In the process I found that U20 pin 1 must go to ground. It might help to remove R25 too.
  6. Right. As it stands you could have two 256K boards plus one 64K in 1064 mode for a total of 576K.
  7. Looks like the board is already designed to handle 256K. Just plug in some 41256 DRAMs instead of 4164s, and plug a 74LS153 into U20 and you're good. (This will also require the newer ANTIC.)
  8. My warning has nothing to do with bank switching, only with refreshing. The schematic says 4164 RAMs (7 bits refresh), and that's what the board needs. Daisy chaining, eh? Interesting.
  9. Thanks for the schematic. I'm surprised to see two busses, one on P1 and another on P2. What's the second bus for? Either way the 4264 needs 8 bits of refresh address and the older ANTIC supplies only 7. All 600XLs had the newer ANTIC and would be OK, but many 800XLs had the older one, so they could fail.
  10. Please post the 64K board schematic so that I can confirm this warning.
  11. Be careful there. The 4264 needs 256 cycle refresh and so won't work correctly with the older ANTIC chips. Also MT branded RAMs have a poor reputation.
  12. 3 of us worked on the project. DT wrote the 8048 disassembler, LW did the hardware, I did the firmware. We called it the Circular Buffer for Lengthy Written Data Transfer.
  13. At work in the 80s we had a similar printer buffer for the PC's parallel port. It also had a large IC which was an Intel 8048, an early microcontroller. We reverse engineered it and extended it to 256K using the 8748 EPROM-based version of Intel's microcontroller. In your photo the large IC has a Zilog logo, so it could be a Z8 microcontroller.
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