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HP Portable Plus - ROMBO 128 KB EPROMS?
07-20-2020, 07:28 AM (This post was last modified: 10-31-2021 06:53 PM by Martin Hepperle.)
Post: #3
RE: HP Portable Plus - ROMBO 128 KB EPROMS?
I figured that I only need these connections:
Code:
from       to
socket    EPROM    
  22         2      former OE/ to A16 (with jumpers (A) this is A16 from the CPU bus)
  28        32     VCC to VCC (rerouted)
 GND        24    new OE/, always enabled
additional new pins
Code:
VPP    1   n.c. or ground?
P/    31   n.c. or VCC?

The jumpers (A) and (B) control how the address lines A15 ad A16 are connected to the ROM/EPROMs. All in position (A) direct A15 and A16 to the socket pins A15 resp. OE/.
This is the same setting as used for the 64 KByte EPROMs.
I have to evaluate whether a 27C1001 on a PCB still fits the space before resorting to some PLCC chip. Maybe for starting some lifted pins and flying wires are o.k., but not nice for repeated EPROM programming.

Chip pinouts:

Code:

   64 KByte                       128 KByte
                               VPP    1    32    VCC
                               A16    2    31    P/
A15    1    28    VCC          A15    3    30    n.c.?
A12    2    27    A14          A12    4    29    A14
A7     3    26    A13          A7     5    28    A13
A6     4    25    A8           A6     6    27    A8
A5     5    24    A9           A5     7    26    A9
A4     6    23    A11          A4     8    25    A11
A3     7    22    OE/, VPP     A3     9    24    OE/
A2     8    21    A10          A2    10    23    A10
A1     9    20    CE/          A1    11    22    CE/
A0    10    19    Q7           A0    12    21    Q7
Q0    11    18    Q6           Q0    13    20    Q6
Q1    12    17    Q5           Q1    14    19    Q5
Q2    13    16    Q4           Q2    15    18    Q4
VSS   14    15    Q3           VSS   16    17    Q3
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RE: HP Portable Plus - ROMBO 128 KB EPROMS? - Martin Hepperle - 07-20-2020 07:28 AM



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