Department of Computer Scien

ce and Information Engineering

National Cheng Kung University

HANEL

INTERFACING EXTERNAL

ROM

P0 and P2 in Providing Address

‰Since the PC (program counter) of the 8031/51 is 16-bit, it is capable of accessing up to 64K bytes of program code

¾In the 8031/51, port 0 and port 2 provide the 16-bit address to access external memory

ƒP0 provides the lower 8 bit address A0

• A7, and

P2 provides the upper 8 bit address A8

• A15

ƒP0 is also used to pr

ovide the 8-bit data bus

D0 –

D7

¾P0.0

– P0.7 are used for both the address

and data pathsƒaddress/data multiplexing

P1.0P1.1P1.2P1.3P1.4P1.5P1.6P1.7RST(RXD)P3.0(TXD)P3.1(INT0)P3.2(INT1)P3.3(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