Hi Ranjit,

You make the call of the subroutine REQUEST_PRINT and in at least in one place you call REQUEST_PRINT again (in body of it) without RETurning from REQUEST_PRINT (See your code fragment). It is recursion I think. 

Franc Urbanc is quite right: your stack is overflowing for that. 

Bye, Igor

ENCLOSURE: Ranjit code fragment.
..........................
START:   ACALL INIT_PORTS
             ACALL REQUEST_PRINT
             SJMP  START
..........................
REQUEST_PRINT:
             ACALL PWR_ON  ; MOVE THE BOARD
             CLR   FULL  ; REQ. FOR HALF STEP MODE
             CLR   DIR  ; SET A DIRECTION
             JNB   I4,MIN_POS
             JNB   I3,MAX_POS
             MOV   R6,#54
             ACALL ERROR_DUMP ; CANNOT PRINT, HEAD OUT OF POSITION
MIN_POS: MOV R6,#06H
             ACALL DUMP_HOST
             MOV   R6,#2FH
             ACALL DUMP_HOST
             CLR   DIR
             SJMP  CONT_HITAM
MAX_POS: MOV R6,#06H
             ACALL DUMP_HOST
             MOV   R6,#2BH
             ACALL DUMP_HOST
             SETB  DIR
CONT_HITAM: ACALL INIT2
             ACALL RECEIVE
             CJNE  A,#'.',NOT_QUIT
             ACALL PWR_OFF
NOT_QUIT: CJNE A,#'T',NOT_PRINT
..........................
NOT_PRINT: LJMP RESTART
..........................
RESTART:
L1:         MOV   R5,#0H
             SETB  HIGH_CURRENT
             ACALL INIT1
             MOV   A,#'>'  ; COMMAND PROMPT
             ACALL SEND
COMMAND: ACALL INIT2
             ACALL RECEIVE
             CJNE  A,#'.',NOT_DOT ; REQUEST TO POWER DOWN
             ACALL PWR_OFF
NOT_DOT: CJNE A,#05H,NOT_06
             ACALL INITIALIZE_MOTOR; REQUEST TO INITIALIZE MOTOR
NOT_06: CJNE A,#35H,NOT_05 ; REQUEST TO PRINT
             ACALL REQUEST_PRINT
NOT_05: SJMP L1