VIC-20 32k memory expansion (ver. 951026)

by Adam Bergström (adam.bergstrom@um.erisoft.se)

This is one of my contributions to the Commodore 8-bit community. I made this document to show you how to expand the memory of your VIC-20. I designed and built the memory expansion in October 1995.

I have built the expansion on a vero-board inside my VIC-20, so the cartridge port is free. All that is seen outside are three switches (reset, write enable/disable, memoryexpansion on/off).

I also plan to make an external memory-cartridge (so I can make some for my friends without opening their precious babies) as soon as I get all the stuff to make PCB:s at work.

This new version has removed the trouble with bus-collision.

I hope that this document is accurate and that you can get it to work. My hardware DOES work, and has been tested on quite a few programs, both expanded, unexpanded, and cartridgeimages (both 8k and 16k).

I will take no responsibility for any damages that may occur when you are trying to use this information. This information is free, and any damages are done by you, not me.

Let the old 8-bit computers LIVE ON!

Features

32k RAM in four 8k blocks located in memory at:
- $2000 (BLK1)
- $4000 (BLK2)
- $6000 (BLK3)
- $A000 (BLK5)
This gives you an additional 24k BASIC memory (27,5k total!), and 8k at the cartridge area.
Ability to load and run cartridge-images from disk or tape.
Write enable/disable switch, lets you run copy protected cartridge images.
Switch to enable/disable the whole extra-memory, to let you use an external cartridge, or use the VIC-20 unexpanded.
Reset switch.

Parts used

1 * HY62256, 32kbyte static RAM, 100ns (any 32k SRAM faster than 500ns should be O.K.)
1 * 74LS147, 10-4 line priority encoder
2 * on/off switches
1 * reset switch
Some wires and a vero-board to solder all parts on.

How to connect it all

SRAM_X is pin nr X on SRAM.  74_X   is pin nr X on 74LS147.  VIC_X  is pin nr X on VIC expansion port.  SWITCHX_Y is switch nr X, pin nr Y.    SWITCH1 is write enable/disable.  SWITCH2 is expansion enable/disable.  SWITCH3 is reset.    SRAM_1(A14)  - 74_9(A)  SRAM_2(A12)  - VIC_R(CA12)  SRAM_3(A7)   - VIC_K(CA7)  SRAM_4(A6)   - VIC_J(CA6)  SRAM_5(A5)   - VIC_H(CA5)  SRAM_6(A4)   - VIC_F(CA4)  SRAM_7(A3)   - VIC_E(CA3)  SRAM_8(A2)   - VIC_D(CA2)  SRAM_9(A1)   - VIC_C(CA1)  SRAM_10(A0)  - VIC_B(CA0)  SRAM_11(D0)  - VIC_2(CD0)  SRAM_12(D1)  - VIC_3(CD1)  SRAM_13(D2)  - VIC_4(CD2)  SRAM_14(GND) - VIC_GND  SRAM_15(D3)  - VIC_5(CD3)  SRAM_16(D4)  - VIC_6(CD4)  SRAM_17(D5)  - VIC_7(CD5)  SRAM_18(D6)  - VIC_8(CD6)  SRAM_19(D7)  - VIC_9(CD7)  SRAM_20(!CE) - 74_6(C)  SRAM_21(A10) - VIC_N(CA10)  SRAM_22(!OE) - 74_6(C)  SRAM_23(A11) - VIC_P(CA11)  SRAM_24(A9)  - VIC_M(CA9)  SRAM_25(A8)  - VIC_L(CA8)  SRAM_26(A13) - 74_7(B)  SRAM_27(R/W) - VIC_18(CR/W)  SRAM_28(VDD) - VIC_21(+5V)    74_1(4)      - VIC_10(!BLK1)  74_2(5)      - VIC_11(!BLK2)  74_3(6)      - VIC_12(!BLK3)  74_4(7)      - VIC_13(!BLK5)  74_5(8)      - SWITCH1_2  74_6(C)      - SRAM_20(!CE) + SRAM_22(!OE)  74_7(B)      - SRAM_26(A13)  74_8(GND)    - VIC_GND  74_9(A)      - SRAM_1(A14)  74_10(9)     - SWITCH2_2  74_11(1)     - VIC_GND  74_12(2)     - VIC_GND  74_13(3)     - VIC_GND  74_14(D)     - NC  74_15(NC)    - NC  74_16(VCC)   - VIC_21(+5V)    SWITCH1_1    - VIC_18(CR/W)  SWITCH1_2    - 74_5(8)  SWITCH1_3    - VIC_21(+5V)    SWITCH2_1    - VIC_GND  SWITCH2_2    - 74_10(9)  SWITCH2_3    - VIC_21(+5V)    SWITCH3_1    - VIC_GND  SWITCH3_2    - VIC_X(RESET)

Memory expansion port, seen from the back of the VIC-20

1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
A  B  C  D  E  F  H  J  K  L  M  N  P  R  S  T  U  V  W  X  Y  Z

   1 - GND                   A - GND
   2 - CD0                   B - CA0
   3 - CD1                   C - CA1
   4 - CD2                   D - CA2
   5 - CD3                   E - CA3
   6 - CD4                   F - CA4
   7 - CD5                   H - CA5
   8 - CD6                   J - CA6
   9 - CD7                   K - CA7
  10 - !BLK1                 L - CA8
  11 - !BLK2                 M - CA9
  12 - !BLK3                 N - CA10
  13 - !BLK5                 P - CA11
  14 - !RAM1                 R - CA12
  15 - !RAM2                 S - CA13
  16 - !RAM3                 T - I/O2
  17 - VR/W                  U - I/O3
  18 - CR/W                  V - SO2
  19 - !IRQ                  W - !NMI
  20 - NC                    X - !RESET
  21 - +5V                   Y - NC
  22 - GND                   Z - GND

Static memory HY62256 (SRAM), pin configuration

      +---U---+
  A14-|1    28|-VDD
  A12-|2    27|-R/W
   A7-|3    26|-A13
   A6-|4    25|-A8
   A5-|5    24|-A9
   A4-|6    23|-A11
   A3-|7    22|-!OE
   A2-|8    21|-A10
   A1-|9    20|-!CE
   A0-|10   19|-D7
   D0-|11   18|-D6
   D1-|12   17|-D5
   D2-|13   16|-D4
  GND-|14   15|-D3
      +-------+

74LS147, pin configuration

      +---U---+
    4-|1    16|-VCC
    5-|2    15|-NC
    6-|3    14|-D
    7-|4    13|-3
    8-|5    12|-2
    C-|6    11|-1
    B-|7    10|-9
  GND-|8     9|-A
      +-------+

On/off switch

        /
        /
     --+--
     |   |
     |   |
     -----
     | | |
     1 2 3

How to contact me

Snail mail:: Adam Bergström
Storgatan 92,2
903 33 Umeå
SWEDEN
Telephone:: +46-90-178490 begin_of_the_skype_highlighting +46-90-178490 FREE end_of_the_skype_highlighting
Internet email:: adam.bergstrom@um.erisoft.se

VIC-20 Internal 32K Memory Expansion