Maybe the pull-ups on pins 8 and 9 are not needed... Old habits are hard to break.

Code:
' Write to file
        FAT_src[0] = "A"
        FAT_src[1] = $d
        FAT_src[2] = $a
        FAT_src[3] = "B"
        FAT_src[4] = $d
        FAT_src[5] = $a
        FAT_src[6] = "C"
        FAT_src[7] = $d
        FAT_src[8] = $a
     FAT_src[9] = $d
     FAT_src[10] = $a 
        FAT_count = 11
    Gosub FSfwrite
    Serout2 PORTC.6, 84, [ "Write ", Dec FAT_error, $d, $a]
    If (FAT_error != 0) Then Stop