title "2WireLCD - Write 'Hello' to an LCD using 2 Wires" ; ; This Code Sends the data to the LCD in 4 Bit mode and ; writes the string: "Hello". ; ; The data is shifted out to a 74LS174 with The High Order Bit being a "Gate" ; Bit connected to the LCD's "E" line. The next Highest Bit goes to the ; LCD's "RS" Bit. The lowest Bit goes to D4 (and each Bit is higher from ; there). ; ; ; Hardware Notes: ; Reset is tied directly to Vcc and PWRT is Enabled. ; The PIC is a 16C84 Running at 4 MHz. ; PortA.0 is the Data Bit ; PortA.1 is the Clock Bit ; ; ; Data Being Sent looks like: ; ; Clear S/R Shift Data Strobe ; ; 旼컴컴컴컴컴컴� 旼컴컴컴컴컴컴커 ; � � � � ; ; 旼컴컴컴컴캇굇굇굇굇� 悶 ; Data 컴컴컴컴컴컴컴� 컴컴牡컴 ; 컴왯왯왯왯왯왯컴컴컴컴커悶悶悶悶悶旼컴컴컴� ; Clock 잎잎잎잎잎잎 잎잎잎잎잎잎 ; 悶 ; E 컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸읕� ; ; Shift Data: ; Bit 1 - Always High (Gate for "E") ; Bit 2 - RS Bit ; Bit 3 - LCD D4 ; Bit 4 - LCD D5 ; Bit 5 - LCD D6 ; Bit 6 - LCD D7 ; ; Myke Predko ; 99.03.13 ; LIST P=16C84, R=DEC ; 16C84 Runs at 4 MHz errorlevel 0,-305 INCLUDE "p16c84.inc" ; Register Usage CBLOCK 0x00C ; Start Registers at End of the Values Dlay ; 8 Bit Delay Variable Temp ; Temporary Value Used When Sending Out Data NOTemp ; Temporary Value to "NybbleOutput" ENDC ; Define Inforation #DEFINE Data PORTA,0 #DEFINE Clock PORTA, 1 ; Macros ClockStrobe MACRO ; Strobe the Data Bit bsf Clock bcf Clock ENDM EStrobe MACRO ; Strobe the "E" Bit bsf Data bcf Data ENDM PAGE __CONFIG _CP_OFF & _XT_OSC & _PWRTE_ON & _WDT_OFF ; Note that the WatchDog Timer is OFF ; Demo Code, Loop Forever Toggling PA0 (Flashing the LED) org 0 clrf PORTA movlw 0x01C ; Enable PA0 & PA1 for Output bsf STATUS, RP0 movwf TRISA ^ 0x080 bcf STATUS, RP0 call Dlay5 ; Wait 20 msecs before Reset call Dlay5 call Dlay5 call Dlay5 bcf STATUS, C ; Clear Carry (Instruction Out) movlw 0x03 ; Reset Command call NybbleOut ; Send the Nybble call Dlay5 ; Wait 5 msecs before Sending Again EStrobe call Dlay160 ; Wait 160 usecs before Sending the Third Time EStrobe call Dlay160 ; Wait 160 usecs before Sending the Third Time bcf STATUS, C movlw 0x02 ; Set 4 Bit Mode call NybbleOut call Dlay160 movlw 0x028 ; Note that it is a 2 Line Display call SendINS movlw 0x008 ; Turn off the Display call SendINS movlw 0x001 ; Clear the Display RAM call SendINS call Dlay5 ; Note, Can take up to 4.1 msecs movlw 0x006 ; Enable Cursor Move Direction call SendINS movlw 0x00C ; Turn the LCD Back On call SendINS clrf FSR ; Output the Message OutLoop movf FSR, w ; Get the Offset to Output incf FSR call Message iorlw 0 ; At the End of the Message? btfsc STATUS, Z goto Loop ; Yes - Equal to Zero call SendCHAR ; Output the ASCII Character goto OutLoop Loop ; Loop Forever when Done goto Loop ; Subroutines Message ; Message to Output addwf PCL ; Output the Characters dt "Hello", 0 SendCHAR ; Send the Character to the LCD movwf Temp ; Save the Temporary Value swapf Temp, w ; Send the High Nybble bsf STATUS, C ; RS = 1 call NybbleOut movf Temp, w ; Send the Low Nybble bsf STATUS, C call NybbleOut return SendINS ; Send the Instruction to the LCD movwf Temp ; Save the Temporary Value swapf Temp, w ; Send the High Nybble bcf STATUS, C ; RS = 0 call NybbleOut movf Temp, w ; Send the Low Nybble bcf STATUS, C call NybbleOut return NybbleOut ; Send a Nybble to the LCD movwf NOTemp ; Save the Nybble to Shift Out swapf NOTemp ; Setup to Output to the High Part of the Byte movlw 6 ; Clear the Shift Register movwf Dlay NOLoop1 ClockStrobe decfsz Dlay goto NOLoop1 bsf Data ; Put out the Gate Bit ClockStrobe bcf Data ; Put out the RS Bit rlf PORTA ClockStrobe movlw 4 ; Now, Shift out the Data movwf Dlay NOLoop2 rlf NOTemp ; Shift Through the Nybble to Output bcf Data ; Clear the Data Bit (which is the Clock) rlf PORTA ; Shift the Carry into the Shift Register ClockStrobe decfsz Dlay goto NOLoop2 EStrobe ; Strobe out the LCD Data return Dlay160 ; Delay 160 usecs movlw 256 - ( 160 / 4 ) ; Loop Until Carry Set addlw 1 btfss STATUS, C goto $-2 return Dlay5 ; Delay 5 msecs movlw 4 ; Set up the Delay movwf Dlay movlw 256 - 0x0E8 addlw 1 btfsc STATUS, Z decfsz Dlay goto $-3 return end