Here is the layout of the VIC20 RAM expansion:
VIC 20 74LS11 62256
VR/W ----------------------------------------------- WE
RAM 1 ---------------------- 4
RAM 2 ---------------------- 5
RAM 3 ---------------------- 3
6 ----- s1 ----|---- OE,CS
8 ----- s1 ----|
BLOCK 1 ------- s2 --------- 9
BLOCK 2 ------- s3 ------ 10,1,2
BLOCK 3 ------- s4 ------- 11,13
12 ------------------- A14
+5V -------- s2,s3,s4
A0-A13 ---------------------------------------- A0-A13
D0-D7 ------------------------------------------ D0-D7
Explanation:
RAM 1, RAM 2 and RAM 3 are OR'ed together to produce the 3K select.
BLOCK 1, BLOCK 2 and BLOCK 3 are OR'ed to produce the select above 8K.
BLOCK 2 and BLOCK 3 are OR'ed to produce A14
s1, s2, s3 and s4 are pairs of DIP switches.
s1 selects between 3K expansion or expansion above 8K.
s2, s3 and s4 select individual 8K blocks.
+5V is provided to pull the unselected 8K block select lines high,
although they are not usually needed
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