CompuPro RAM board settings

From: Frank McConnell <>
Date: Fri Dec 20 00:23:00 2002

Richard Cini wrote:
> I just got a CompuPro RAM20 memory board with no manual. I'm looking
> for the DIP switch settings specifically, but a copy of the manual would be
> very helpful.

And here I was kicking myself for forgetting to take the CompuPro
Product User Manuals volumes back out to storage where they would be
buried in boxes all the way at the back. My forgetfulness is your
good luck tonight.

> It's missing two chips...a 74LS74 at U6 and a 25LS2521 at U10. The
> memory array is 8 columns of 8 chips, type MM2147J. I'm thinking that these
> are 2kx1 chips, resulting in a 16k board.

No, it's a 32KB board. 8 rows of 4KB each. Your "missing" ICs are
explained below too.

Switch 1 enables 4K blocks, one position per row.
   SW1-1: row 0 ON enables row;
   SW1-2: row 1 OFF disables row
   SW1-8: row 7

Switch 2:
   Positions 1-4 set the base address of the board on a 4KB boundary.
     SW2-1 is the least significant bit, SW2-4 is the most significant,
     write your desired start address in binary and then a 1 means
     turn the switch on and 0 means turn it off. So OFF OFF OFF OFF
     means the board starts at 0x0000, ON OFF OFF OFF at 0x1000, ....
   Position 5: ON: RAM XX is a standard/global memory
               OFF: RAM XX is to be used as extended address or bank
                    select memory
   Position 6: ON: enables response (deselect) to PHANTOM
               OFF: disables response to PHANTOM
   Positions 7 and 8 matter if the board is being used as a bank
   select memory. If you want the board to come up enabled when
   you turn on the computer, SW2-7 should be on and SW2-8 should be off.
   If you want the board to come up disabled, SW2-7 should be off and
   SW2-8 should be on. Never leave them both on or both off.

Switch 3:
  If you are using the board as extended address memory,
  put the 25LS251 in position U11 and leave positions U6 and U10
  blank. (This is why you're missing a couple ICs!) Then,
  Switch 3 sets bits A16 through A23 of the extended address.
    SW3-1: address bit A16 ON = 1,
    SW3-2: address bit A17 OFF = 0
    SW3-8: address bit A23
  If you are using the board as a bank select memory, put the
  25LS251 in position U10 (leaving U11 blank) and put a 74LS74
  into position U6. Then, Switch 3 sets the bank select port
    SW3-1: port address bit A0 ON = 1,
    SW3-2: port address bit A1 OFF = 0
    SW3-8: port address bit A7

Switch 4:
  If you are using the board as a bank select board, Switch 4
  sets the data bit(s) that will enable the board when written
  to the bank select port.
    SW4-1: data bit D0 ON = 1,
    SW4-2: data bit D1 OFF = 0
    SW4-8: data bit D7
  Note that if more than one switch is set, then the board will
  be enabled if *any* bit matches.

-Frank McConnell
Received on Fri Dec 20 2002 - 00:23:00 GMT

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