DSEG AT 30h ;this tells the compiler to start placing data from 30h NrValues EQU 8 ;const nrvalues=8; OldValues: DS NrValues ;reserve space for OldValues RPin: DS 1 ;reserve space for RPin (a counter) AStore: DS 1 ;reserve space where A will be stored temporarily CSEG ;now we tell the compiler that we are going to write code ORG 0 MOV P3,#255 ;Making P3 Output Port MOV OldValues+0,#255 ;Initilising memory locations for storing output MOV OldValues+1,#255 ;from the 8 latches MOV OldValues+2,#255 ;and loading them with initial values MOV OldValues+3,#255 ;which indicate all signals are low MOV OldValues+4,#255 MOV OldValues+5,#255 MOV OldValues+6,#255 MOV OldValues+7,#255 ;three nested loops needed: one for the bits, one for the 8 bytes, one which repeats the all infinitely LOOP: MOV R0,#OldValues+7 ;location R0 is Rlatch POLL: MOV A,R0 ADD A,#-OldValues ;calculate latch Nr MOV P1,A ;set the latch Nr for the decoder MOV RPin,#8 ;there are 8 bits in a byte MOV A,P3 ANL A,@R0 ;ANDing A with the locations 8 to 1 which will store CPL of P3 CHKPIN: RLC A ;Get the Pins thatwent form LOW to HIGH JC WRITE GETBAK: DJNZ RPin,CHKPIN MOV A,P3 ;Since the output is latched, it has not changed since last time CPL A MOV @R0,A ;Moving the data of the respective latches to the respective registers ; following line not needed if it is initialised at the beginning of the loop ; MOV 10,#8 ;ReInitialising Rpin value as 8 for next loop ;following line replaced by 2 lines as R0 won't point into 1..8 any more ; DJNZ R0,POLL DEC R0 CJNE R0,#OldValues-1,POLL ;again no need ; MOV R0,#8 ;ReInitilising value of Rlatch as 8 for next loop JMP LOOP ;repeat infinitely this loop WRITE: MOV AStore,A ;storing the value of A in 20 for further use MOV A,R0 ADD A,R0 ;Adding contents of R0 to A seven more times ADD A,R0 ;I read that using MUL always clears the flag ADD A,R0 ;And I dont want to do that ADD A,R0 ADD A,R0 ADD A,R0 ADD A,R0 ADD A,10 MOV P3,A MOV A,AStore ;Returning A its original Value JMP GETBAK END