====== Sending a command to a disk drive, the easy way ======
The easiest way of sending a command to the disk drive is by simply using the command string as filename when calling OPEN.
BASIC code:
OPEN 15,8,15,"I":CLOSE 15
Assembler code:
LDA #cmd_end-cmd
LDX #cmd
JSR $FFBD ; call SETNAM
LDA #$0F ; file number 15
LDX $BA ; last used device number
BNE .skip
LDX #$08 ; default to device 8
.skip LDY #$0F ; secondary address 15
JSR $FFBA ; call SETLFS
JSR $FFC0 ; call OPEN
BCS .error ; if carry set, the file could not be opened
.close
LDA #$0F ; filenumber 15
JSR $FFC3 ; call CLOSE
JSR $FFCC ; call CLRCHN
RTS
.error
; Akkumulator contains BASIC error code
; most likely errors:
; A = $05 (DEVICE NOT PRESENT)
... error handling for open errors ...
JMP .close ; even if OPEN failed, the file has to be closed
cmd: .TEXT "I" ; command string
cmd_end:
====== Sending a command to a disk drive, the flexible way ======
Another way of sending a command to the disk drive is by leaving the filename string empty and send the command string afterwards. The advantage of this is that you can send several commands but only open the command channel one time.
BASIC code:
OPEN 15,8,15:PRINT#15,"I":CLOSE 15
Assembler code:
LDA #$00
LDX #$00
LDY #$00
JSR $FFBD ; call SETNAM (no filename)
LDA #$0F ; file number 15
LDX $BA ; last used device number
BNE .skip
LDX #$08 ; default to device 8
.skip LDY #$0F ; secondary address 15
JSR $FFBA ; call SETLFS
JSR $FFC0 ; call OPEN
BCS .error ; if carry set, the file could not be opened
LDX #$0F ; filenumber 15
JSR $FFC9 ; call CHKOUT (file 15 now used as output)
LDY #$00
.loop LDA cmd,y ; get byte from command string
JSR $FFD2 ; call CHROUT (send byte through command channel)
INY
CPY #cmd_end-cmd
BNE .loop
.close
LDA #$0F ; filenumber 15
JSR $FFC3 ; call CLOSE
JSR $FFCC ; call CLRCHN
RTS
.error
; Akkumulator contains BASIC error code
; most likely errors:
; A = $05 (DEVICE NOT PRESENT)
... error handling for open errors ...
JMP .close ; even if OPEN failed, the file has to be closed
cmd: .TEXT "I" ; command string
.BYTE $0D ; carriage return, needed if more than one command is sent
cmd_end: