SUBROUTINE ENI101(LUN,IER)

C
C	ENABLE INTERROGATE PROTOCOL
C
	LOGICAL*1 REC(3)

	DATA ITRMAX /3/				!MAX NUM OF RETRIES AFTER '?'

	ITRY=-1
5	NR=3
	ITRY=ITRY+1
	CALL IO101(LUN,'I',1,REC,NR,IER)	!SEND 'I' AND WAIT FOR REPLY
	IF(IER.NE.1) GO TO 1000
	IF(NR.NE.3) GO TO 910			!REPLY SHOULD BE <CR>,<LF>,'*'

	IF(REC(1).EQ.13.AND.REC(2).EQ.10.AND.REC(3).EQ.42) GO TO 1000

	IF(REC(3).EQ.63.AND.ITRY.LT.ITRMAX) GO TO 5

900	WRITE(6,905) REC,ITRY
905	FORMAT(/' *** FATAL *** [ENI101] NO "CR,LF,*" AFTER ',I2,'RETRIES: '
     $,3O5)
	GO TO 999
910	WRITE(6,915) NR,(REC(I),I=1,NR)
915	FORMAT(/' *** FATAL *** [ENI101] NUMBER OF CHARACTERS RECEIVED: '
     $,I5/15X,10O4)

999	IER=0
1000	RETURN
	END