OSBYTE &B9 (185) - Read/Write MOS copy of palette register/ROM polling semaphore
On the BBC, B+ and Master, this contains the MOS's copy of the palette register in the video ULA. On the Electron there is no video ULA, and this location contains the ROM polling semaphore. When the semaphore is non-zero the 100Hz ROM service call &15 is sent to ROMs. The semaphore is normally accessed with *FX23 to increment it and *FX24 to decrement it.
- OSBYTE &16 - Increment ROM polling semaphore
- OSBYTE &17 - Decrement ROM polling semaphore
- OSBYTE &B3 - Master ROM polling semaphore location
- Paged ROM service calls
Jgharston 22:30, 26 May 2009 (UTC)