Re: Commodore to S-Video or HDMI video?

Mia Magnusson wrote:

> Many VIC 20 cartridges starts with the picture decentered to the upper 
> left corner, and needs to be moved with the cursor keys. 

That only really applies in case Terry Raymond has a PAL VIC-20, which I 
strongly doubt as he resides in the USA.

The reason the picture appears in the upper left corner is because the 
NTSC version of the VIC-I chip has different value ranges for screen 
positioning compared to the ranges used by the PAL version of the same 
chip. The Kernel contains default values suitable for respective video 
chip, but many cartridges - both Commodore's own and third party ones - 
don't trust the built-in firmware ROMs and instead hard code the default 
settings of the VIC-I chip.

As long as you run a cartridge on a NTSC VIC-20, you usually won't 
notice a difference because the values in the cartridge ROM may be 
identical to the ones in the Kernel. Sometimes the number of columns or 
rows, or positioning the screen is slightly changed.

However when you put in the same cartridge in a PAL VIC-20, the code 
will tell the VIC-I chip to configure the screen far into the upper left 
corner. Commodore themselves realized they had made a boo-boo and 
usually included a routine that lets you move the screen into visible 
area. Third party manufacturers didn't care. Many of the latter 
cartridges have been patched to exist in PAL version (just a different 
set of VIC-I configuration values) or even read the values from Kernel 
where applicable.

But back to Terry's problem, if the BASIC screen displays correct both 
on the LCD and a 1084, but cartridges won't display on the LCD but still 
work on the 1084, something weird is going on. Off-hand, I can't think 
of what could cause that.

Best regards

Anders Carlsson