RE: VIC-20 memory expansion

From: COPLIN, Nicholas. (ncoplin_at_orbeng.com.au)
Date: 2000-09-06 05:23:34

many thanks!

> -----Original Message-----
> From:	William Levak [SMTP:wlevak@cyberspace.org]
> Sent:	Wednesday, 6 September 2000 11:18
> To:	cbm-hackers@dot.tcm.hut.fi
> Subject:	Re: VIC-20 memory expansion 
> 
> 
> 
> 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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