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

Parts used

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

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

How to contact me

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