The 8051 Microcontroller and Embedded

Department of Computer Scien

ce and Information Engineering

National Cheng Kung University, TAIWAN

8255 HANEL

INTERFACING

LCD

Connection To The 8255

(cont

;New command write subroutine with checking busy flagNCMDWRT:MOV R2,A ’)

;save a value

MOV A,#90H

;PA=IN to read LCD status

MOV R0,#CNTPORT ;load control reg addressMOVX @R0,A

;configure PA=IN, PB=OUT

MOV A,#00000110B ;RS=

0,R/W=1,E=1 read command

MOV R0,#BPORT ;load port B addressMOVX @R0,A ;RS=0,

R/W=1 for RD and RS pins

MOV R0,#APORT ;load port A address

READY: MOVX A,@R0

;read command reg

PLC A ;mo

ve D7(busy flag) into carry

JC READY

;wait until LCD is ready

MOV A,#80H ;m

ake PA and PB output again

MOV R0,#CNTPORT ;load control port addressMOVX @R0,A ;i

ssue control word to 8255

MOV A,R2

;get back value to LCD

MOV R0,#APORT ;load port A address MOVX @R0,A ;issue

info to LCD’s data pins

MOV R0,#BPORT ;load port B address MOV A,#00000100B ;RS=

0,R/W=0,E=1 for H-To-L

MOVX @R0,A ;activ

ate RS,R/W,E pins of LCD

NOP

;make E pin pulse wide enough

NOPMOV A,#00000000B ;RS=

0,R/W=0,E=0 for H-To-L

MOVX @R0,A ;latch

in LCD’s data pin info

RET

Program 15-2. (cont’)