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base:reading_the_directory [2015-04-17 04:33] (current)
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 +====== Reading the directory ======
 +
 +Just a simple routine which reads the directory file from a device and prints it to screen.
 +
 +<​code>​
 +        LDA #​dirname_end-dirname
 +        LDX #<​dirname
 +        LDY #>​dirname
 +        JSR $FFBD      ; call SETNAM
 +
 +        LDA #$02       ; filenumber 2
 +        LDX $BA
 +        BNE .skip
 +        LDX #$08       ; default to device number 8
 +.skip   LDY #$00       ; secondary address 0 (required for dir reading!)
 +        JSR $FFBA      ; call SETLFS
 +
 +        JSR $FFC0      ; call OPEN (open the directory)
 +        BCS .error ​    ; quit if OPEN failed
 +
 +        LDX #$02       ; filenumber 2
 +        JSR $FFC6      ; call CHKIN
 +
 +        LDY #$04       ; skip 4 bytes on the first dir line
 +        BNE .skip2
 +.next
 +        LDY #$02       ; skip 2 bytes on all other lines
 +.skip2 ​ JSR getbyte ​   ; get a byte from dir and ignore it
 +        DEY
 +        BNE .skip2
 +
 +        JSR getbyte ​   ; get low byte of basic line number
 +        TAY
 +        JSR getbyte ​   ; get high byte of basic line number
 +        PHA
 +        TYA            ; transfer Y to X without changing Akku
 +        TAX
 +        PLA
 +        JSR $BDCD      ; print basic line number
 +        LDA #$20       ; print a space first
 +.char
 +        JSR $FFD2      ; call CHROUT (print character)
 +        JSR getbyte
 +        BNE .char      ; continue until end of line
 +
 +        LDA #$0D
 +        JSR $FFD2      ; print RETURN
 +        JSR $FFE1      ; RUN/STOP pressed?
 +        BNE .next      ; no RUN/STOP -> continue
 +.error
 +        ; Akkumulator contains BASIC error code
 +
 +        ; most likely error:
 +        ; A = $05 (DEVICE NOT PRESENT)
 +exit:
 +        LDA #$02       ; filenumber 2
 +        JSR $FFC3      ; call CLOSE
 +
 +        JSR $FFCC     ; call CLRCHN
 +        RTS
 +
 +getbyte:
 +        JSR $FFB7      ; call READST (read status byte)
 +        BNE .end       ; read error or end of file
 +        JMP $FFCF      ; call CHRIN (read byte from directory)
 +.end
 +        PLA            ; don't return to dir reading loop
 +        PLA
 +        JMP exit
 +
 +dirname:
 +        .TEXT "​$" ​     ; filename used to access directory
 +dirname_end:​
 +</​code>​
  
base/reading_the_directory.txt ยท Last modified: 2015-04-17 04:33 (external edit)