OSBYTE &87
OSBYTE &87 (135) - Character at text cursor and screen MODE. Called by BASIC's =MODE function.
On exit X=character at current cursor position (or 0 if unreadable)
Y=current mode number (shadow modes DO NOT return with bit 7 set)
The returned value does not give the shadow MODE bit. The following code will return the full MODE number that can be used with the MODE command to re-select the same mode:
mode%=(FNfx(&87,0)DIV256) OR ((FNfx(&75,0)AND&10)*8) ... DEFFNfx(A%,X%):LOCAL Y%:Y%=X%DIV256:=((USR&FFF4)AND&FFFF00)DIV256
LDA #&75:JSR OSBYTE :\ Read VDU status TXA:AND #&10:CMP #&10 :\ Test shadow flag in bit 4 PHP :\ Save shadow flag in Carry LDA #&87:JSR OSBYTE :\ Read current MODE TYA:ASL A:PLP:ROR A :\ Move shadow flag into bit 7
According to the B+ User Guide, the call typically takes 120 microseconds. To save time, the base mode number can be obtained without character recognition by calling OSBYTE &A0 with X=&55.
See Also
- MODE
- OSBYTE &75
- OSBYTE &A0
- Reading screen mode
- Paging in video memory
- http://mdfs.net/Docs/Comp/BBC/Osbyte80
Jgharston 22:01, 26 May 2009 (UTC) Jgharston (talk) 08:08, 28 December 2016 (UTC) Jgharston (talk) 23:39, 4 February 2017 (UTC)
