MOV  TMOD,#01100000B     ;counter 1,mode 2,C/T=1 
                                   ;external pulses         
          MOV  TH1,#0              ;clear TH1
          SETB P3.5                ;make T1 input 
AGAIN:    SETB TR1                 ;start the counter
BACK:     MOV  A,TL1               ;get copy of count TL1
          MOV  P2,A                ;display it on port 2
          JNB  TF1,Back            ;keep doing it if TF=0
          CLR  TR1                 ;stop the counter 1
          CLR  TF1                 ;make TF=0 
          SJMP AGAIN               ;keep doing it