Hello

I'm trying to define my screen mode by writing into the CRTC registers and the video ULA. The problem I'm having is that it appears to work for a few frames, then it would appear to have the teletext bit set again in the video ULA.

If I re-write my value into the video ULA each frame it sort of works but occasionally there'll be a flash of teletext(!). Does anyone know what causes the BBC to do this? I don't really want to write into that register every frame.

Cheers.

Do you have some sample code to illustrate the problem?

Also, are you trying this on a real BBC or under emulation?

Kind regards,

Francis.

It's under (BeebEm) emulation.

I'm pushed a bit today at work but I'll try and get some sample code knocked up tomorrow.

The OS rewrites the ULA control every few frames for flashing colours. Either set a graphics mode before rewriting all the registers (rather than doing it from mode 7) and put up with colours 8-15 flashing, disable all interrupts, or stop the vsync interrupt from getting to the OS (using IRQ1V).

Or use *FX 154,n to write to the Video ULA, which also updates the OS's copy that is rewritten every flash period.

Aha! Cheers wizards!