Re: A session with my VIC-20

From: Levente Hársfalvi (
Date: 1999-08-20 19:05:11


> 1. My 1084S monitor (which I use with the Amiga) has trouble with
>    vertical sync (I think it is called - the picture is scrolling
>    from top to bottom) on CVBS signal when the border colour is light.
>    I.e. the startup cyan/white combination will scroll and colour
>    is gone, but if I do "POKE36879,24" to get black/white, the screen
>    is stable and colours re-appear.

My TV acted the opposite earlier (now I use a C= 1801). Especially when
I set border to black and paper to white. Maybe mine detected an 'extra'
vertical retrace signal, because of a wrong sync signal trigger level
threshold. Should it be something similar?...

> 2. My 3/16/24/32K expansion card seems to finally have died. I tried
>    to clean the weared connectors, but without success. What can one
>    do to bring it back to life again, if it only is the connector
>    pins that are damaged? Otherwise, I'd have to build my own card
>    as there is a description on the net.

Just one remark. I designed a PCB for your memory expansion circuit
(with small additions, like the highest 8K can be mapped to the low 3K)
and it should go to Funet soon or later. But I should first correct it,
'cos I mis-measured the distance between the pins; the board works
however, but it should be corrected before letting anyone to re-build

> 4. I have been scanning and OCR:ing some VIC-20 manuals (all in Swedish)
>    these last days - they will appear on iDOC= later. However, when I
>    proofread the manual for Super Expander, it said the prg uses a
>    1024x1024 matrix, and every pixel on the screen is eight dots high
>    and eight dots wide, which should imply 128x128 resolution in hires.
>    The manual doesn't state the exact resolution. Someone else told me
>    the resultion is much higher, and I didn't get an opportunity to try
>    this (mainly because of #2 above).

I have an original super expander card and the documentation. It states
that the expander supports both hi-res and multicolor graphics modes
(even mixed mode, when the character color determines the mode on a
position). The resolution is 160x160 in hi-res and 80x160 in multicolor

>    What I can't understand is how 1024/160 equals eight. Any clue?

Maybe the same way as some early Data Becker books stated that the
highest freq of the SID should be 8200 Hz...

> My VIC chip is 6561E, and I could dig out the model numbers of the
> other chips too, if someone thinks that is useful. I don't remember
> the serial number, but it is < 10000, the machine has this two-plug
> power connector but the "modern" layout of keys.

My first Vic-20 (Vic-20 CR, DIN PS connector, VIC-20 label instead of
German VC-20) also had a 6561E (1782, in the bottom side 61,
Philippines, 141101U, 1582). Unfortunately, some parts should have been
dead in it (it forgot to reset the character memory position pointer
when starting the screen refresh).

...Does anybody know any other 6561 versions than the 6561-101? The E
should be measured a bit closer if it's different in functionality.


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