OSBYTE &80
OSBYTE &80 (128) - Read I/O device or buffer status
On entry, If XY<0, read buffer status
If XY>=0, read I/O device
On exit XY=returned value
| XY on entry | XY on exit |
| 0 | b0-b7=buttons, b8-b15=last ADC channel converted |
| 1 | Analogue Channel 1 |
| 2 | Analogue Channel 2 |
| 3 | Analogue Channel 3 |
| 4 | Analogue Channel 4 |
| 5 | Mouse X boundary |
| 6 | Mouse Y boundary |
| 7 | Mouse X position |
| 8 | Mouse Y position |
| 9 | Mouse button state, b0=Left, b1=Middle, b2=Right |
| 127 (128-1) | low level read from buffer -1 - ie 16-bit GET (cZ80Tube, Brandy and others) |
| &FFFF (-1) | Keyboard buffer |
| &FFFE (-2) | Serial input buffer |
| &FFFD (-3) | Serial output buffer |
| &FFFC (-4) | Printer output buffer |
| &FFFB (-5) | Sound output buffer 0 |
| &FFFA (-6) | Sound output buffer 1 |
| &FFF9 (-7) | Sound output buffer 2 |
| &FFF8 (-8) | Sound output buffer 3 |
| &FFF7 (-9) | Speech output buffer |
| &FFF6 (-10) | Mouse input buffer |
| &FFF5 (-11) | MIDI input buffer {check} |
| &FFF4 (-12) | MIDI output buffer {check} |
Calling from BBC BASIC
=ADVAL() calls OSBYTE &80
Implementations
If an unknown device or buffer is examined, then the call is passed to sideways ROMs as an Unknown OSBYTE service call. {check: some exceptions}
Most implementations only actually check bit 7 of the parameter (ie, bit 7 of X) to chose between reading devices and reading buffers, so for instance ADVAL(255) is the same as ADVAL(-1).
Mouse
Most mouse drivers do not implement calls 5, 6 and 9. The VFS Videodisk Filing System ROM used with the Domesday System implements 5, 6 and 9. The mouse buttons are more usually read with INKEY-10, INKEY-11 and INKEY-12. 8-bit systems rarely implement a mouse buffer. 32-bit systems usually use a sound system that does not use these sound output buffers.
Jgharston 18:59, 11 September 2007 (BST) Jgharston (talk) 06:54, 21 December 2018 (CET)
