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BUHBYE.SYSTEM: Work around MouseText bug on Franklin ACE 2X00/500 systems

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Joshua Bell 2021-11-03 19:55:52 -07:00
parent a7e32d62d4
commit 8dbdd58d38
1 changed files with 20 additions and 0 deletions
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20
selectors/buhbye.system.s
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@ -601,6 +601,26 @@ handy_rts2:
pla
sta INVFLG
;; Work around MouseText deactivation bug on Franklin ACE 2X00/500
;; The Apple IIe/IIc/IIgs and the Franklin ACE 2X00/500 all use the
;; screen hole address $4FB to store a video firmware operating
;; mode byte, e.g. whether or not MouseText output is active. For
;; the Apple IIe and IIgs, see the Apple IIe Technical Reference
;; Manual, Appendix J Monitor Firmware Listing for the definition.
;; (Bit 0 is set when MouseText is inactive and clear when active.)
;; The Apple IIc also uses bit 0 the same way, but bits 3 and 7 are
;; also normally set. The Franklin Ace 2X00 and 500 set bit 6
;; when MouseText mode is activated by printing $1B, but fails to
;; clear it when printing $18, so MouseText remains active. This
;; seems to be a bug in the firmware. Work around it by detecting
;; the unique byte signature left behind and resetting it.
lda $4FB ; $4FB = $30 normally (V flag clear)
cmp #$40 ; $4FB = $70 if MT is active (V flag set)
bne :+ ; $4FB = $40 if you try to disable MT!
lda #$30 ; Bug in firmware? We're not sure yet.
sta $4FB ; Any way, set it manually.
:
;; Draw the name
name: jsr space
jsr update_curr_ptr