sjc@mordor.UUCP (03/28/84)
This is a response to recent pleas for documentation on the Xerox 820, a
version of the Big Board CP/M system which the Xerox Outlet Store ((214)
960-3367) has been selling for $50 per board.
Digital Research Computers
PO Box 401565
Garland, TX 75040
(214) 271-3538
For $5 they will send you a nice packet of schematics plus theory
of operation plus directions on using their EPROM monitor. However,
the Xerox version differs from theirs in at least three ways: parts
are positioned and numbered differently on the board, connector
pinouts are rearranged, and the last stages of the CRT driver have
been redesigned.
B.G. Micro
PO Box 280298
Dallas, TX 75228
(214) 271-5546
These people advertise in the March "Nuts and Volts" magazine that
they will sell you a blank copy of the Xerox 820 board with EPROMS
and "complete schematics" for $29.95 plus $2 shipping. Perhaps you
could persuade them to sell you the schematics alone. I have not
dealt with them.
Xerox
1341 Mockingbird Lane
Dallas, TX 75247
Attn: Bonnie Campbell
The "820 Information Processor Development Guide", part number
9R80368, is available for $40. It is not clear whether this
contains software information, hardware information, both, or
neither. We have one of these on order.
We also have schematics on order from a third source whose address I do
not have with me at the moment. I will post information to the net as
soon as I get it, so the best advice I can offer is to sit tight for a
week or so.
Meanwhile, anyone who has already gotten CP/M to run on an 820 board could
do us all a great service by posting pinouts, advice on the BIOS, etc.
Incidentally, I purchased a switching power supply for the 820 board from the
Xerox Outlet Store for $50. It offers all the voltages the board needs, but
lacks the +24V needed for 8" floppies.--Steve
(S-1 Project, Lawrence Livermore National Laboratory)
MILNET: sjc@s1-c UUCP: ...!decvax!decwrl!mordor!sjc
(mailheader return address may not work)sjc@mordor.UUCP (04/03/84)
Thanks to a good samaritan at SRI, I have a copy of some Xerox 820 documentation. For brevity, I will detail primarily the aspects that differ from the original "Big Board" from Digital Research Computers of Texas. Documentation for the original is still available from DRC (214) 271-3538. Xerox 820 documentation (which I haven't seen) is advertised by BG Micro (214) 271-5546. Port Address Decoding: no differences System PIO "A" side: Bit0 DVSEL 1 Bit1 DVSEL 2 Bit2 Side Bit3 Keyboard data available Bit4 8"/5.25" disk select Bit5 Assigned for future use Bit6 Display character set (?) Bit7 Bank switching (0=RAM, 1=ROM & CRT & RAM) Interrupt structures: Monitor uses mode 2 interrupts; I register is loaded with 0FF hex. Priority chain is organized high to low as follows: SIO CHANNEL A SIO CHANNEL B SYSTEM PIO PORT A SYSTEM PIO PORT B GP PIO PORT A GP PIO PORT B CTC CHANNEL 0 CTC CHANNEL 1 CTC CHANNEL 2 CTC CHANNEL 3 General purpose PIO strappings (J11) and pin assignments (J8): J11: odd numbered pins grounded 4 Port B READY polarity 6 Port B lower direction 8 Port A READY polarity 10 Port A upper direction 12 Port B upper direction 14 Port A STROBE polarity 16 Port B STROBE polarity 18 Port A lower direction J8: odd numbered pins are supposed to be grounded; they aren't, so you must ground at least one of them to the PIO chip so as to provide a signal ground to the peripheral device 2 Port A STROBE 4 Port A READY 6 Port A bit 0 ... 20 Port A bit 7 22 Port B STROBE 24 Port B READY 26 Port B bit 0 ... 40 Port B bit 7 CTC Strapping and I/O assignments (J10): System clock 2 1 Clock/trigger 0 ZC-TO0 4 3 Clock/trigger 1 ZC-TO1 6 5 Clock/trigger 2 ZC-TO2 8 7 Clock/trigger 3 Video output connector pin assignments (J7): 6-10 grounded 3 Vertical sync 4 Horizontal sync 5 Video Serial I/O connector pin assignments channel A (J4): 1 Protective ground 2 Transmit data 3 Receive data 4 Request to send 5 Clear to send 6 Data set ready 7 Protective ground 8 Carrier detect 15 Xmit clock 17 Receive clock 20 Data terminal ready Serial I/O strapping options for channel A (J9): No differences Serial I/O connector pin assignments channel B (J3): 1 Ground 2 Receive data 3 Transmit data 4 Clear to send 5 Request to send 6 Data set ready 7 Ground 8 Terminal ready 20 Data carrier detect Keyboard connector pin assignments (J2): 14-25 grounded 1-7 bits 0-7 8 strobe 13 +5 volts via resistor Disk drive connector pin assignments (J1): 20-37 grounded 1 not connected 2 8/5.25 select (grounded for 5.25) 3 not connected 4 index 5 select 1 6 select 2 7 side 8 HDLD 9 step in 10 step 11 write data 12 write 13 trk 00 14 write protect 15 read data 16 low current 17 ready 18 indep pin +12 or anything 19 +5 CRT RAM: 3000 hex through 3FFF hex. I/O ports: 0-3 Channel A baud (writeonly) 4 SIO channel A data 5 SIO channel B data 6 SIO channel A control 7 SIO channel B control 8 GP PIO A data 9 GP PIO A control A GP PIO B data B GP PIO B control C-F Channel B baud (writeonly) 10 1771 status/command 11 1771 track 12 1771 sector 13 1771 data 14-17 CRT scroll register if 1, then loc 3000 is at bottom line; if 2, then loc 3000 is next to bottom line; if 17, then loc 3000 is top line, etc. 18 CTC 0 19 CTC 1 1A CTC 2 1B CTC 3 1C system data 1D system control 1E keyboard data 1F keyboard control Power (J5): 1 -12 2 +12 CPU 3 +12 disk 4-6 ground 7 +12 8 +5 9 +5 Power fed out to monitor (if needed) (J6): 1 ground 2 +12 Original Xerox 820 disk formats: 8" 5.25" Tracks 77 40 Sectors 26 18 Bytes/sector 128 128 Tracks reserved 2 3 for OS Capacity 241K 81K 5.25" format is CROMEMCO format, 8" is IBM 3740 format Monitor entry points are alleged to be the same as the DRC big board.o Monitor commands are alleged to be the same, except: Test command is "X", not "T" Verify command is missing Boot command is "A", not "B" A "T" command connects the keyboard to the printer port like a "typewriter" Setting MSB of displayed character gives blinking attribute. --Steven Correll (S-1 Project, Lawrence Livermore National Laboratory) MILNET: sjc@s1-c UUCP: ...!decvax!decwrl!mordor!sjc (mailheader return address may not work)
Dbennett%xmm-plexus01.amc@amc-hq.arpa (08/15/85)
Does anyone know where I can obtain modification information for the Xerox-820 computer. Such as Double Density Mod, Hard Disk Mod, etc. I have two Xerox-820 computers on order and plan on using them for Packet Gateway capability and Packet Bulletin Board . Also are there any monthly publications out there for the Xerox-820.
CRC.DlosLV%xerox.arpa@amc-hq.arpa (08/16/85)
Probably the best source of information for the 820 is a magazine called "Micro Cornucopia". There have been many articles about the things you mentioned in back issues. Micro Cornucopia P.O. Box 223 Bend, OR 97709 (503) 382-8048 Other than that, we have published a few minor items in our VIP newsletter here in the Vendor Programs Group at Xerox, Lewisville, TX. Nothing of a highly technical nature though. Chuck Carpenter
bobh@pedsgd.UUCP (Bob Halloran) (08/21/85)
Organization : Perkin-Elmer DSG, Tinton Falls NJ In article <724@brl-tgr.ARPA> Dbennett%xmm-plexus01.amc@amc-hq.arpa writes: >Does anyone know where I can obtain modification information for the Xerox-820 >computer. Such as Double Density Mod, Hard Disk Mod, etc. I have two Xerox-820 >computers on order and plan on using them for Packet Gateway capability and >Packet Bulletin Board . > >Also are there any monthly publications out there for the Xerox-820. The best magazine I know of for 820 hackers is Micro Cornucopia. They publish bi-monthly, and have a regular 820 column. Many vendors for the 820/Big Board market seem to advertise there. They can be reached at POB 223, Bend OR 97709, (503)382-8048. Good luck. Bob Halloran Sr MTS, Perkin-Elmer DSG ============================================================================= UUCP: {ihnp4, decvax, ucbvax}!vax135!petsd!pedsgd!bobh USPS: 106 Apple St M/S 305, Tinton Falls NJ 07724 DDD: (201) 758-7000 Disclaimer: My opinions are my own. Quote: "History is made at night. Character is what you are in the Dark."