Extra memory for a VIC-20 - problems

From: Ruud_at_Baltissen.org
Date: Sun, 28 Apr 2013 19:14:44 +0200
Message-ID: <517D5904.22740.373820@Ruud.Baltissen.org>
Hallo allemaal,

I really started soldering again: expanding a VIC-20 (with C64 power 
plug up) to 32 KB SRAM. I have done that several times before so 
that shouldn't be a problem. But it didn't work out this time: the 
Vic-20 died under my hands :(

So I took another board and repeated all steps. First I removed the 
BASIC-ROM and soldered it on top of the System-ROM. Plus a wire from 
CS to pin 9 of UC5. Things worked fine.
I placed a 24 -> pin convertor on the place where first the 
BASIC-ROM was seated. Made all needed connection and tested things: 
fine. Then I placed a 74LS11, 3*3AND, that should combine all RAMx 
and BLKx (except BLK5) signals. I placed the SRAM, CS line connected 
to +5V, still fine. 
Now I connected CS to RAM1 and I got a weird number for the amount 
of RAM: somewhere between the original 3583 and expected 4709 bytes. 
Replacing the SRAM solved the problem...... for just 20 seconds: 
freese. It took me a quarter to find out I hadn't connected the CS 
line to RAM1 (= pin14) but to pin 15, the one that goes to the two 
onboard 2114, 1024*4, SRAMs.

Two SRAMs parallel to each other can cause problems. BUT THEN WHERE 

Then I saw my error and connected the CS line to RAM1: rubbish on 
the screen. I connected it to RAM2: again rubbish. Connected it to 
RAM3: nice screen, 4709 bytes free. Had to have dinner so I typed in 
and ran a little Basic program in the mean time. 
I started to use the AND gates and first added RAM2 and then RAM1. 
Worked out fine. 

But the above means that the order to add RAM is 3, 2, 1. Was that 
known? (not to me)

Kind regards / Met vriendelijke groet, Ruud Baltissen

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Received on 2013-04-28 18:00:04

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