SUBROUTINE SNDBLK(FILE, BYTECT, BLOCK)
C************************************************************
C
C  THIS ROUTINE IS USED TO SEND EACH INDIVIDUAL BLOCK
C  OF A DISPLAY FILE TO THE GT40.
C
C  FILE   - CONTAINS THE DISPLAY FILE (PACKED FOUR
C           BYTES(8-BIT) TO THE WORD)
C  BYTECT - NUMBER OF BYTES IN FILE
C  BLOCK  - CURRENT BLOCK NUMBER
C
C  POSSIBLE ERRORS: (ALL ERRORS ARE FATAL AND RETURN BLOCK = 0)
C	?BAD BYTE COUNT (BLOCKS MUST BE LESS THAN "200 BYTES)
C	?INVALID REPLY TO AN ADD COMMAND
C	?INVALID REPLY TO A BLOCK
C
C  ROUTINES CALLED:
C	SEND   - SEND A COMMAND TO THE GT40
C	GET    - RECEIVE A COMMAND FROM THE GT40
C	SETTTY - SET TERMINAL CHARACTERISTICS FOR I/O
C	GFIELD - BYTE FETCH FUNCTION
C	SNDCHR - SEND AN IMAGE CHARACTER TO GT40
C	ERROR  - ERROR LOGGING ROUTINE
C
C************************************************************
	IMPLICIT INTEGER (A - Z)
	INTEGER FILE(BYTECT)

	BCT = BYTECT
	START = (BLOCK - 1) * "170 + 1
100	END = START + "167
	IF(END .LE. BCT) GO TO 200
	END = BCT

C  TRANSMIT THE ADD COMMAND
200	START = START + 20
	END = END + 20
	SIZE = END - START + 2
	CALL SEND(11, SIZE, 0, 0)
	CALL GET(STATUS, X, Y, DNUM)
	IF(STATUS .EQ. "66) GO TO 200
	IF(STATUS .EQ. 11) GO TO 400

	IF(STATUS .NE. 12) GO TO 300
	CALL ERROR('?BAD BYTE COUNT =', SIZE)
	BLOCK = 0
	RETURN
300	CALL ERROR('?INVALID REPLY DURING ADDBLK, STATUS =', STATUS)
	BLOCK = 0
	RETURN
C  ADD COMMAND SUCCESSFUL, SEND BLOCK
400	CSUM = 0
	CALL SETTTY
	CALL SNDCHR(2)
	DO 500 I = START,END
	  WORD = I / 4
	  IF(MOD(I,4) .NE. 0) WORD = WORD + 1
	  POS = MOD(I,4)
	  IF(POS .EQ. 1) BYTE = GFIELD(FILE(WORD), 10, 8)
	  IF(POS .EQ. 2) BYTE = GFIELD(FILE(WORD), 2, 8)
	  IF(POS .EQ. 3) BYTE = GFIELD(FILE(WORD), 28, 8)
	  IF(POS .EQ. 0) BYTE = GFIELD(FILE(WORD), 20, 8)
	  CSUM = CSUM + BYTE
	  CALL SNDCHR(BYTE)
500	CONTINUE

	CSUM = -CSUM .AND. "377
	CALL SNDCHR(CSUM)
	CALL GET(STATUS, X, Y, DNUM)
	IF(STATUS .EQ. "66) GO TO 100
	IF(STATUS .EQ. 15) RETURN

	CALL ERROR('?INVALID REPLY TO A BLOCK, STATUS =', STATUS)
	BLOCK = 0
	RETURN
	END