APPENDIX ELEVEN



     Another method to check for sector use is to see if byte 125
     ($7D) shows a sector has data in it; if not zero, it is being used (it
     records the number of bytes used in a sector). You can examine
     the sector contents by adding PRINT SEC$ after the read.

     PRINT PEEK(771) after reading a sector will display the status; 1
     means good, any other number means bad. Check for bad sec-
     tors by PEEKing here after any sector read.

     The above routine with a few modifications will print a list of all
     the sectors on a disk with data in them (best directed to your
     printer, but I use the screen display in the example below). This
     is a slow and inelegant routine, but you can easily rework it for
     your own use.

     5 DIM SEC$(128),CHK$(128),CNT(720)
     10 DATA 104,32,83,228,96
     15 SEC$(1)=CHR$(0):SEC$(128)=SEC$:SEC$(2)=S
        EC$:CHK$(1)=CHR$(0):CHK$(128)=CHK$:CHK$(
        2)=CHK$
     16 REM SETS UP ARRAY SPACE AND FILLS IT
     17 REM CHK$ IS FULL OF BLANK SPACES - CONTE
        NTS OF UNUSED SECTORS
     18 FOR L00P=0 TO 720:CNT(LOOP)=0:REM EMPTY
        ARRAY
     20 FOR N=1536 TO 1540:READ X:POKE N,X:NEXT
        N
     25 REM THIS
     30 POKE 769,1:POKE 770,82
     35 TRAP 100
     40 FOR SNUM=1 TO 720
     50 POKE 778,SNUM-(INT(SNUM/256)*256):POKE 7
        79,INT(SNUM/256)
     51 REM POKES LSB, MSB OF SECTOR INTO 778, 7
        79
     55 BUFFER=ADR(SEC$):BUFFL=BUFFER-(INT(BUFFE
        R/256)*256):BUFFH=INT(BUFFER/256)
     56 POKE 772,BUFFL:POKE 773,BUFFH
     60 Z=USR(1536)
     70 IF SEC$=CHK$ THEN CNT(SNUM)=0:NEXT SNUM:
        GOTO 100
     80 CNT(SNUM)=SNUM:NEXT SNUM
     100 FOR LOOP=1 TO 720
     110 IF CNT(LOOP)=0 THEN NEXT LOOP:GOTO 150
     120 PRINT CNT(LOOP);" ";:NEXT LOOP
     150 END

     To copy one sector to another, use the routine below. Add a
     loop routine to copy more than one at a time. This routine
     copies all 128 bytes, including the three "record" bytes.