Department of Computer Scien

ce and Information Engineering

National Cheng Kung University

HANEL

INTERFACING EXTERNAL

ROM

P0 and P2 in Providing Address

(cont’)

‰ALE (address latch enable) pin is an output pin for 8031/51

¾ALE = 0, P0 is used for data path¾ALE = 1, P0 is used for address path

74LS373 D Latch

‰To extract the address from the P0 pins we connect P0 to a 74LS373 and use the ALE pin to latch the address

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