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Re: Get a board Xerox 820-II working fine

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  • enrlaz
    Some answers first: Wow, just like me in the 80s. Perhaps it s the same kit ? Did it include the 3 EPROMS? A: I not know: I bought this one:
    Message 1 of 4 , Apr 11, 2013
      Some answers first:
      Wow, just like me in the 80s.
      Perhaps it's the same "kit"?
      Did it include the 3 EPROMS?
      A: I not know: I bought this one: http://www.ebay.it/itm/Vintage-Xerox-820-II-Motherboard-/330719705046

      I started gathering the parts but gave up because
      - just the cost of the sockets would've been prohibitive
      - the entire unit in cabinet with keyboard, CRT
      went surplus so cheap that even I valued my time enough
      to get one and just give up.
      A: I'd love to buy a complete system, but in Italy that appears rarely on internet and it cost SOOOOOO much AND buying in USA and adding its shipping it would cost SOOOOOO MUCH

      Well below what it happens from the last my post:

      I sent the post at least 10 days ago, but I saw that it was only released today.
      Since then there have been other more events with VCF.

      1) how to convert ps2 to parallel interface: look here http://www.vintage-computer.com/vcforum/showthread.php?32129-Ferguson-Big-Board-1-monitor-rom&highlight=kyeakel i attached the schematic and the pic 16f84 code. here it assembled for my xerox 820-I board i put in a classic PC case http://www.flickr.com/photos/67772736@N07/7419081302/in/set-72157630233712582/

      2) xerox 820-II Floppy disk controller card: as i told i bought an ALONE xerox 820-II motherboard. i discovered that i need a FDC card. It's not easy to find. It's schematic is at the end of the xerox 820-II service manual here: http://classiccmp.org/dunfield/miscpm/x820serv.pdf (it is not much readabe). Then i find some pics on Internet of this FDC card: http://www.vintage-computer.com/vcforum/attachment.php?attachmentid=12294&d=1363516923 AND , I discovered the presence of an IC named 733w01522 (U1) on the photo of the original PCB i can't idenfiy and also i cannot read on the schematic not very readable
      reported at the end of xerox820-II service manual.

      Thanks for contribution of Chuck Guzis from the VCF he told me that the 733w01522 is a PROM and it is equivalent at 74S288 but also to others IC as reported here http://www.hobbyroms.com/proms.html.

      U1 (74S288) and U2 (74S174) together constitute a "finite state machine" (so they told to me cause I'm not so expert) whose purpose is to provide a read clock and a read data to the chip WD1797 from raw data received from the drive.

      Then I need to discover the code to insert into that chip (without having the original chip programmed with me!).

      Upon the recommendation of Chuck Guzis I found the code listing on page 12 of the manual of the FDC1797's application notes http://bitsavers.informatik.uni-stuttgart.de/pdf/westernDigital/FD179X_Application_Notes_Jun80.pdf . At this point, trusting to this code I'd need to buy a programmed 74S288 (or equivalent).

      After all this I was finally trying to figure out if it sould be better to use of a schematic published on an old issue of Microcornucopia: https://www.dropbox.com/s/4f8kblogrlzdr9m/FDC_from_Micro_Cornucopia_%2322_Feb85.pdf Who so far wrote that article decided to build himself a FDC controller card for his xerox 820-II extracting a block of its schematic from a Kaypro-II's
      schematic really making very few changes and using a FDC WD1793 + WD9216 for external separator data.

      Due to its small number of components, and having already a spare kaypro II working board with WD1793 and its WD9216 all seems a bit more simple buying a connector like this http://www.futureelectronics.com/en/technologies/interconnect/connectors-pcb/header-plug-board-mount/Pages/9795113-EBM36MMNN.aspx , a perfboard an mounting components lie shown in the pic on the microcornucopia's article. Of course i'll look for the FDC on Internet, but a people told me: If you know what this thing is, you probably need it and i added: if you NOT know what it is you'll throw it away easly.

      Enrico - Pisa (ITALY)
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