Assembler: CBM prg Studio.
Hi guys, Merry Christmas and happy holidays :) What is going on with the text output in my interupt? I must be missing something obvious here but please take a look at the attached picture...
It is supposed to say:
"Moving into range of the first candidate..."
*Bitmap displays
"COMMENCE MINE Y/N?"
Take a look at the attached image and see for yourself.
Below is the code. Thanks for taking the time out to take a look, this has been baffling me all night!
:) JamesClick here to see the pic
; 10 SYS (2064)
*=$0801
BYTE $0E, $08, $0A, $00, $9E, $20, $28, $32, $30, $36, $34, $29, $00, $00, $00
;Sexy Subroutines...
CHROUT = $FFD2 ; Output a character to the screen
SCNKEY = $FF9F ; Place ASCII character into keyboard queue
GETIN = $FFE4 ; Places the ASCII value into the Accumulator
PLOT = $FFF0 ; PLOTs the cursor to the next line down, X = the row number
; Y = the colum. Always Clear the Carry (CLC) vital for
; plotting!
DECDIS = $BDCD
;The stack location for temporary strings...
tempst1 = $0020
tempst2 = $0021
;Screen details...
Screen = $0400
Border = $D020
Background = $D021
; I/O Stuff.........
LSTX = $00c5 ; Current key pressed.
; 01=ENTER. 3C=SPACE. 1=38. 2=3b. 3=08. 4=0b. 5=10. 6=13. 7=18. 8=1b. 9=20
; Y=19. N=27. S=0d. P=29.
*=$0810
lda #147 ; This is a BASIC routine that presses the keyboard
jsr CHROUT ; button that clears the screen.
lda #00
sta Border
sta Background
jsr Init ; Split the screen!
ldx #$00
lda #$0e
jsr CHROUT
ldx #20
ldy #00
clc
jsr PLOT
lda #>Siliconi
sta tempst2
lda #<Siliconi
sta tempst1
jsr print
ldx #01
ldy #00
clc
jsr PLOT
lda #>message
sta tempst2
lda #<message
sta tempst1
jsr print
loaddccimage
;lda $3f40,x
;sta $0400,x
lda $4040,x
sta $0500,x
lda $4140,x
sta $0600,x
;lda $4240,x
;sta $0700,x
;lda $4328,x
;sta $d800,x
lda $4428,x
sta $d900,x
lda $4528,x
sta $da00,x
;lda $4628,x
;sta $db00,x
inx
bne loaddccimage
lda #$3b
sta $d011
lda #$18
sta $d016
jump jmp *
;===================
Init SEI ; set interrupt bit, make the CPU ignore interrupt requests
LDA #%01111111 ; switch off interrupt signals from CIA-1
STA $DC0D
AND $D011 ; clear most significant bit of VIC's raster register
STA $D011
LDA $DC0D ; acknowledge pending interrupts from CIA-1
LDA $DD0D ; acknowledge pending interrupts from CIA-2
LDA #0 ; set rasterline where interrupt shall occur
STA $D012
LDA #<Irq ; set interrupt vectors, pointing to interrupt service routine below
STA $0314
LDA #>Irq
STA $0315
LDA #%00000001 ; enable raster interrupt signals from VIC
STA $D01A
CLI ; clear interrupt flag, allowing the CPU to respond to interrupt requests
RTS ; ?? Leave here ??
Irq LDA $D011 ; select text screen mode
AND #%11011111
STA $D011
lda #$14
sta $d018
LDA #%00000000
sta $d016
LDA #<Irq2 ; set interrupt vectors to the second interrupt service routine at Irq2
STA $0314
LDA #>Irq2
STA $0315
LDA #100
STA $D012 ; next interrupt will occur at line no. 0
ASL $D019 ; acknowledge the interrupt by clearing the VIC's interrupt flag
JMP $EA31 ; jump into KERNAL's standard interrupt service routine to handle keyboard scan, cursor display etc.
Irq2 LDA $D011 ; select bitmap screen mode
ORA #%00100000
STA $D011
lda #$18
sta $d018
LDA #%00010000
sta $d016
LDA #<Irq ; set interrupt vectors back to the first interrupt service routine at Irq
STA $0314
LDA #>Irq
STA $0315
LDA #200
STA $D012 ; next interrupt will occur at line no. 210
ASL $D019 ; acknowledge the interrupt by clearing the VIC's interrupt flag
JMP $EA81 ; jump into shorter ROM routine to only restore registers from the stack etc
Print
ldy #0 ;Clear the Y register
Print1
lda (tempst1),y
cmp #255
beq PrintDone
jsr PrintChar
iny
jmp Print1
PrintDone
RTS
PrintChar
cmp #48
bcc PrintChar1
PrintChar1
jsr CHROUT
rts
Siliconi
Text "COMMENCE MINE Y/N?"
byte 255
message
Text "Moving into range of the first candidate..."
byte 255
*=$1FFE
incbin "ASTRO1.prg"
The issue seems to relate to the feature of the PETSCII specification called shifting.
Assuming the graphics mode is unshifted, PETSCII has only uppercase letters in its powerup state.
In the shifted mode, the lowercase characters a-z occupy the same character space (0x41..0x5a) as the upper case characters A-Z in the unshifted mode. In this mode the upper case characters are located at (0x61..0x7a), which holds some graphical glyphs in the unshifted mode.
The evidence supports this, since the lower case letters are visualised as uppercase and the uppercase letters are shown as block graphics characters.
To solve this:
On C64 the sets are alternated by flipping bit 2 of the byte 53272
Alternatively I think it's possible to output the right character directly to the screen memory without using the KERNAL function. I'm not sure about this, since it's been quite a long time when I programmed C64. It might have been that instead the toggling of the character set needed to be disabled so that random key presses didn't alter the screen...