Try to make these two correction to your code:

Code:
MAIN:
HSERIN 10,Skip00, [DEC4 hr]

B0 = HR
D0 = B0 DIG 0                    
READ D0,DIGIT[0]
D0 = B0 DIG 1
READ D0,DIGIT[1]
D0 = B0 DIG 2
READ D0,DIGIT[2]
D0 = B0 DIG 3
READ D0,DIGIT[3]

Skip00:

for index = 0 to 3
seg = digit [index]
SHIFTOUT SDO,SCLK,0,[SEG\8]
PORTA.0[index] = 1
PAUSEus 999
PORTA=0
NEXT INDEX

goto main
Al.