A session with my VIC-20

From: Carlsson, Anders (dal95acn_at_mds.mdh.se)
Date: 1999-08-20 08:52:33

Hi, all.

Yesterday evening, I decided to pull out my VIC-20 from the pedestal,
to check a few things I had forgotten with it. This is a session log:

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.

   I opened the monitor to see if there is some knob I could adjust,
   but found none. I had this monitor on service previously, as it
   didn't work at all. Before I had that breakdown, CVBS signal was

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.

3. Shamus on original ROM still works great... :-)

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 also own some stand-alone books in Swedish for the VIC-20, written
   by Sune Windisch from Förlagsgruppen. In one chapter he describes the
   Super Expander, and claims the resolution in hires is 160x160 pixels.
   That would mean 10 double-height rows times 20 columns, 3200 bytes of
   memory for user-defined graphics.

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

5. As a result of pondering about screen resolution, I poked (literaly)
   around, tweaking my monitor to scale down the picture as much as
   possible, adjust the picture to extreme X and Y coordinates, and
   use $9000-$9003 to get the most of the VIC chip. These are the
   numbers I got:

   $9000 : Minimum 5 (4 shows half-width characters in the leftmost
	   column), maximum 61 (similar effect for 62)

   $9001 : Minimum 13 (10-12 works, but on my monitor, the top scan
	   lines get distorted), maximum 15x something.

   $9002 : Maximum 27 (or almost-28) characters wide.

   $9003 : Maximum 36 rows high.

   That would imply a theoretical maximum resolution of 27x36, but this
   is obviously too much for the VIC chip to display, as the screen
   begun to flicker and jump heavily. Maybe my monitor caused some of 

   I lowered to 27x32, and got a stable screen. However, when I moved
   the screen with $9001, the screen suddenly began to jump again.
   This only happens on single Y-positions of the screen.

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.

Grumble. And my IEC cable is broken, and my "bigger" Amiga has a
defunct parallel port, so I couldn't use the IEC cable even if it
was ok. Oh well, I could use my old Amiga 500+ as I did before.

/Anders Carlsson
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