Department of Computer Scien

ce and Information Engineering

National Cheng Kung University, TAIWAN

I/O HANEL

PROGRAMMING

Port 3(cont’)

‰Port 3 has the additional function of providing some extremely important signals

P1.0P1.1P1.2P1.3P1.4P1.5P1.6P1.7RST(RXD)P3.0(TXD)P3.1(INT0)P3.^2 (I^3 NT1)P3.(T0)P3.4(T1)P3.5(WR)P3.6(RD)P3.7XTAL2XTAL1GND

VccP0.0(AD0)P0.1(AD1)P0.2(AD2)P0.3(AD3)P0.4(AD4)P0.5(AD5)P0.6(AD6)P0.7(AD7)-EA/VPPALE/PROG-PSENP2.7(A15)P2.6(A14)P2.5(A13)P2.4(A12)P2.3(A11)P2.2(A10)P2.1(A9)P2.0(A8)

(^1234567891011121314151617181920)
(^40393837363534333280513130) (8031) 292827262524232221
P3 Bit
Function
P3.0
RxD TxDINT0INT1T0 T1 WRRD
P3.1P3.2P3.3P3.4P3.5P3.6P3.7
Pin 10 11 12 13 14 15 16 17
Serial communicationsExternal interruptsTimersRead/Write signals of external memories
In systems based on 8751, 89C51 or DS89C4x0, pins 3.6 and 3.7 are used for I/O while the rest of the pins in port 3 are normally used in the alternate function role