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Improved device I/O under DOS 3.3

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Certain scenarios (e.g. not running any Applesoft program at all since booting DOS 3.3) can make DOS 3.3 consider cc65 device input (e.g. getchar()) that reads a CR interpreting the command in the keyboard buffer. Setting the hibyte of the Applesoft currently executed line number to some value <> $FF (beside setting the input prompt to some value <> ']') makes DOS 3.3 understand that we're not in intermediate mode and that therefore I/O not preceded with ctrl-d mustn't be fiddled with (see DOS 3.3 routine at $A65E).
This commit is contained in:
Oliver Schmidt 2020-12-19 19:54:12 +01:00
parent 59c58acbe3
commit 0f4cb443b4
2 changed files with 7 additions and 3 deletions
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1
asminc/apple2.inc
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@ -15,6 +15,7 @@ PROMPT := $33 ; Used by GETLN
RNDL := $4E ; Random counter low
RNDH := $4F ; Random counter high
HIMEM := $73 ; Highest available memory address+1
CURLIN := $75 ; Current line number being executed
;-----------------------------------------------------------------------------
; Vectors

9
libsrc/apple2/read.s
View File

@ -19,11 +19,14 @@
.segment "ONCE"
initprompt:
; Set prompt <> ']' to let DOS 3.3 know that we're
; not in Applesoft immediate mode and thus keep it
; from scanning our device I/O for DOS commands.
; Set prompt <> ']' and currently executed Applesoft
; line number hibyte <> $FF to let DOS 3.3 (at $A65E)
; know that we're not in Applesoft immediate mode and
; thus keep it from scanning our device I/O for DOS
; commands.
lda #$80 ; Same value used at $D52C
sta PROMPT
sta CURLIN+1 ; Any value <> $FF will do
rts
.code