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Use ALTCHAR to determine status of 80-col card

This commit is contained in:
Bill Chatfield 2024-02-26 03:14:58 -05:00
parent 0add3cc9d7
commit a6805deddd
1 changed files with 14 additions and 4 deletions
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18
more.merlin.s
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@ -81,7 +81,14 @@ PRODOS_MLI EQU $BF00 ;MACHINE LANG IFACE (MLI)
*
* MEMORY MAPPED I/O: $C000 - $CFFF
*
KBD EQU $C000 ;KEYBOARD DATA AND STROBE
CXROMOFF EQU $C006 ;SELECT SLOT ROMS
CXROMON EQU $C007 ;SELECT INTERNAL ROM
KBDSTRB EQU $C010 ;CLEAR KEYBOARD STROBE
ALTCHAR EQU $C01E ;CHARACTER SET STATUS
RD80VID EQU $C01F ;<=128->40COL, >128->80COL
INVERT EQU $CEDD ;INVERT CHARACTER ON SCREEN
PICK EQU $CF01 ;PICK CHARACTER OFF SCREEN
*
* PRODOS COMMAND CODES
*
@ -343,16 +350,19 @@ MAIN CLD ;CLEAR DECIMAL FLG, AVOID CRASH
* 40 COL OR 80 COL MODE *
* *
********************************
GET_SCRN_WDTH LDA #128
GET_SCRN_WDTH LDA #128 ;USE ALTCHARSET STATUS TO
BIT ALTCHAR ;SEE IF 80-COL CARD TURNED ON
BMI :CARD_ACTIVE ;A 1 IN BIT 7 MEANS ACTIVE
JMP :FORTY_COL ;IF CARD NOT ACTIVE THEN
:CARD_ACTIVE LDA #128 ;SEE IF CARD IS IN 40/80 MODE
CMP RD80VID ;RD80VID <= 128 -> 40 COL
BPL :EIGHTY_COLUMNS ;128 < RD80VID -> 80 COL
LDA #40
:FORTY_COL LDA #40
STA SCR_WDTH
JMP :END
:EIGHTY_COLUMNS LDA #80
STA SCR_WDTH
JSR PRBYTE
:END NOP
:END JSR PRBYTE
RTS
********************************