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;
; Oliver Schmidt, 07.09.2009
;
; unsigned __fastcall__ videomode (unsigned mode);
;
.ifdef __APPLE2ENH__
.export _videomode
.import COUT
.include "apple2.inc"
.segment "LOWCODE"
_videomode:
; Get and save current videomode flag
bit RD80VID
php
; If we are in 80 column mode then the 80 column firmware is
; known to be active so we can just print the ctrl-char code
; (even if this only means staying in the current videomode)
bpl :+
jsr COUT
bra done
; If we are in 40 column mode and want to set 40 column mode
; then we explicitly do nothing as we neither know about the
; current state of the 80 column firmware nor want to fix it
: cmp #$11 ; Ctrl-char code for 40 cols
beq done
; If we are in 40 column mode and want to set 80 column mode
; then we first presume the 80 column firmware being already
; active and print the ctrl-char code (this causes a garbage
; char to be printed on the screen if isn't already active)
jsr COUT
; If we successfully switched to 80 column mode then the 80
; column firmware was in fact already active and we're done
bit RD80VID
bmi done
; The 80 column firmware isn't already active so we need to
; initialize it - causing the screen to be cleared and thus
; the garbage char printed above to be erased (but for some
; reason the cursor horizontal position not to be zeroed)
stz CH
; Initializing the 80 column firmware needs the ROM switched
; in, otherwise it would copy the F8 ROM to the LC (@ $CEF4)
bit $C082
; Initialize 80 column firmware
jsr $C300 ; PR#3
; Switch in LC bank 2 for R/O
bit $C080
; Return ctrl-char code for setting previous
; videomode using the saved videomode flag
done: lda #$11 ; Ctrl-char code for 40 cols
plp
bpl :+
inc a ; Ctrl-char code for 80 cols
: rts ; X was preserved all the way
.endif ; __APPLE2ENH__
|
