Possible to disable character ROM shadowing like on the C128?

johan · Nov 11th 2020

I'm not sure this is the right place to ask, but I wonder if the C65/Mega65 provides a way to disable character ROM shadowing. It was not possible on the C64, but on the C128 you could control it by setting bit 2 in $1/$d9. Being able to disable shadowing makes $1000-$2000 available for your own fonts, which would be helpful on a project I'm working on.

ubik · Nov 11th 2020

By using CHARPTR registers from $D068-$D06A, you can adjust the location of character generator data with byte-level precision. It's possible to use CHARPTR to fetch the font from $1000, or from anywhere else in RAM.

(be sure to enable VIC-IV mode beforehand, and be aware that CHARPTR might get reset when touching legacy VIC-II registers after adjusting CHARPTR without disabling HOTREG first)

mega65 · Nov 11th 2020

Hello,

The C65 doesn't have a mechanism for this, but as ubik mentioned, you don't generally need to do it on the MEGA65, because there are easier ways to move the character data point around. You CAN also change the data in the character "ROM" on the MEGA65, but generally shouldn't need to -- and shouldn't assume that the changes will be kept after freezing.

LG

Paul.

johan · Nov 11th 2020

Good to have confirmation that the character ROMs work like on the C64 and can't be disabled (easily). I should be able to use CHARPTR to find a solution. Thanks!