'c' sets the register right? and 'a' the value of the register? I've been trying to use the small CRTC function to do it but I'm just not seeing any change on the screen. I did have a look at the lesson but I was having a bit of trouble digesting it all, so I thought I'd just try something simple to start with.
I'm guessing it needs more than just this though. Also, I'm not quite sure if I'm calling it in the right place, but I did try it both inside my main loop and beforehand in the screen setup initialisation.
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SET_CRTC: ld c,&03 ; Load Register (&03 = H & V Sync Widths) ld a,134 ; Load value (Set Speccy screen size of 256x192) %10000110 ; - 134 ld b,&bc out (c),c inc b out (c),a RET