Main Index Routine Index Memory Index
Previous Page Next Page


Routine $0604:   Recalibrate head onto Track

This routine moves the Step motor to a lower Halftrack and back to
the upper Track. The loop is always executed twice: first cycle (loop
variable number is even) moves the head to the lower Halftrack, second
moves the head back to the Track. Finally the Drive LED is turned off.
If [$C6]=0 then CF:=1 is returned (error).


JSR from $0484, $054C, Jump from $061B:

0604: C6 C6     DEC $C6        ; initial value is [$C6]=9
0606: F0 FA     BEQ $0602      ; no tries left -> $0602 returns with CF:=1 (error)

0608: A5 C6     LDA $C6
060A: 29 03     AND #$03       ; $071F-Index: 8/7: 0/3, 6/5: 2/1, 4/3: 0/3, 2/1: 2/1
060C: AA        TAX
060D: BC 1F 07  LDY $071F,X    ; Step motor movement ctrl: 8/7: FF/01, 6/5: 01/FF, 4/3: FF/01, 2/1: 01/FF
                               ; FF = move half Track outwards, 01 = move half Track inwards
0610: 20 C2 06  JSR $06C2      ; Move head custom number of Halftracks (+/- Y), set Bit rate.
0613: AA        TAX
0614: 20 F3 06  JSR $06F3      ; Bit shift memory area [$0420-($0420+X)], set [$79]:=$FD.
0617: A5 C6     LDA $C6
0619: 29 01     AND #$01
061B: F0 E7     BEQ $0604      ; if [$C6] value is even -> first loop done -> run second/final loop

061D: AD 00 1C  LDA $1C00
0620: 29 F7     AND #$F7       ; $F7=11110111b: Drive LED = Off
0622: 4C E8 06  JMP $06E8      ; turn Drive LED off, keep everything else (i.e. Bit rate)

    Previous Page / Next Page