Chapter 4 - IO Port Programming IO编程.ppt

PORT 3 For typical I/O use, identical to PORT 1 and 2. Each pin provides a different dual function. Port 3 does not need any pull-up resistors since it already has pull-up resistors internally. Although port 3 is configured as an output port upon reset, this is not the way it is most commonly used. Port 3 has the additional function of providing signals. Serial communications signal：RxD, TxD（Chapter 10） External interrupt：/INT0, /INT1（Chapter 11） Timer/counter：T0, T1（Chapter 9） External memory accesses in 8031-based system：/WR, /RD（Chapter 14） Port 3 Alternate Functions 17 RD P3.7 16 WR P3.6 15 T1 P3.5 14 T0 P3.4 13 INT1 P3.3 12 INT0 P3.2 11 TxD P3.1 10 RxD P3.0 Pin Function P3 Bit ? Accessing Entire Ports MOV A, #0FH MOV P1, A MOV P1, #0F0H XRL P1, #0FFH MOV P1, R0 … Bit Manipulation To toggle every bit of P1 continuously, 3 ways exists: Way 1: Send data to Port 1 through ACC： BACK: MOV A,#55H ;A MOV P1,A ACALL DELAY MOV A,#0AAH ;A MOV P1,A ACALL DELAY SJMP BACK Way 2: Access Port 1 directly： BACK: MOV P1,#55H ;P1 ACALL DELAY MOV P1,#0AAH ;P1 ACALL DELAY SJMP BACK Read-modify-write feature： MOV P1,#55H ;P1 AGAIN: XRL P1,#0FFH ACALL DELAY SJMP AGAIN The instruction XRL P1,#0FFH do EX-OR P1 and FFH （That is, to toggle P1.） Bit Manipulation Sometimes we need to access only 1 or 2 bits of the port instead of the entire 8 bits. This table shows how to name each pin for each I/O port. ? Example: Write a program to perform the following. (a) Keep monitoring the P1.2 bit until it becomes high, (b) When P1.2 becomes high, write value 45H to port 0, and (c) Send a high-to-low (H-to-L) pulse to P2.3. Solution: SETB P1.2 ;make P1.2 an input MOV A,#45H ;A=45H AGAIN:JNB P1.2,AGAIN;get out when P.2=1 MOV P0,A ;issue A to P0 SETB P2.3 ;make P2.3 h