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LCD Interfacing and Programming		325
call	pulseE	; Pulse and delay
; Set RS line for data
bsf	PORTA,RS_line	; RS = 1 for data
call	busyTest ; Busy?
return

;===============================

;first text string procedure ;=============================== storeMSU:

;Procedure to store in PIC RAM buffer the message

;contained in the code area labeled msg1

;ON ENTRY:

;variable pic_ad holds address of text buffer

;in PIC RAM

;w register hold offset into storage area

;msg1 is routine that returns the string characters

;and a zero terminator

;index is local variable that hold offset into

;text table. This variable is also used for

;temporary storage of offset into buffer

;ON EXIT:

;Text message stored in buffer

;

;Store offset into text buffer (passed in the w register)

;in temporary variable

movwf	index	; Store w in index
; Store base address of text buffer in FSR
movf	pic_ad,w ; first display RAM address to W
addwf	index,w	; Add offset to address
movwf	FSR	; W to FSR
; Initialize index for text string access
movlw	0	; Start at 0
movwf	index	; Store index in variable
; w still = 0
get_msg_char:
call	msg1	; Get character from table
; Test for zero terminator
andlw	0x0ff
btfsc	STATUS,Z ; Test zero flag
goto	endstr1	; End of string

;ASSERT: valid string character in w

;store character in text buffer (by FSR)

movwf	INDF	; store in buffer by FSR
incf	FSR,f	; increment		buffer pointer
; Restore table character counter from variable
movf	index,w	;	Get value	into w
addlw	1	;	Bump to next character

326		Chapter 13
movwf	index	; Store table index in
variable
goto	get_msg_char	; Continue
endstr1:
return

; Routine for returning message stored in program area msg1:

addwf	PCL,f	; Access table
retlw	‘M’
retlw	‘i’
retlw	‘n’
retlw	‘n’
retlw	‘e’
retlw	‘s’
retlw	‘o’
retlw	‘t’
retlw	‘a’
retlw	0

;=================================

;second text string procedure ;================================= storeUniv:

;Processing identical to procedure StoreMSU

movwf	index	; Store w in index
; Store base address of text buffer in FSR
movf	pic_ad,0 ; first display RAM address to W
addwf	index,0	; Add offset to address
movwf	FSR	; W to FSR
; Initialize index for text string access
movlw	0	; Start at 0
movwf	index	; Store index in variable
; w still = 0
get_msg_char2:
call	msg2	; Get character from table
; Test for zero terminator
andlw	0x0ff
btfsc	STATUS,Z ; Test zero flag
goto	endstr2	; End of string

;ASSERT: valid string character in w

;store character in text buffer (by FSR)

movwf	INDF	; Store in buffer by FSR
incf	FSR,f	; Increment buffer pointer
; Restore table character counter from variable
movf	index,w	; Get value into w
addlw	1	; Bump to next character
movwf	index	; Store table index in

LCD Interfacing and Programming			327
		;	variable
goto	get_msg_char2	;	Continue
endstr2:
return

; Routine for returning message stored in program area msg2:

addwf	PCL,f	; Access table
retlw	‘S’
retlw	‘t’
retlw	‘a’
retlw	‘t’
retlw	‘e’
retlw	‘,’
retlw	0x20
retlw	‘M’
retlw	‘a’
retlw	‘n’
retlw	‘k’
retlw	‘a’
retlw	‘t’
retlw	‘o’
retlw	0
End

13.4.3 LCDTest3 Program

;File name: LCDTest3.asm

;Date: April 16, 2006

;Author: Julio Sanchez

;Processor: 16F84A

;Description:

;Program to exercise 4-bit PIC-to-LCD interface.

;Code assumes that LCD is driven by Hitachi HD44780

;controller and that the display supports two lines

;each one with 16 characters. The wiring and base

;address of each display line is stored in #define

;statements. These statements can be edited to

;accommodate a different set-up.

;Program uses delay loops for interface timing.

;WARNING:

;Code assumes 4Mhz clock. Delay routines must be

;edited for faster clock

;

; Displays: Minnesota State, Mankato

;

328	Chapter 13

;===========================

;switches ;===========================

;Switches used in __config directive:

;		_CP_ON	Code protection ON/OFF
; *		_CP_OFF
;	*	_PWRTE_ON	Power-up timer ON/OFF

;_PWRTE_OFF

;	_WDT_ON	Watchdog timer ON/OFF
; * _WDT_OFF
;	_LP_OSC	Low power crystal	occilator
; * _XT_OSC		External parallel	resonator/crystal oscillator
;	_HS_OSC	High speed crystal resonator (8 to		10 MHz)
;		Resonator: Murate	Erie CSA8.00MG =	8 MHz
;	_RC_OSC	Resistor/capacitor oscillator
; \|		(simplest, 20% error)

;|_____ * indicates set up values presently selected

;=========================

;set up and configuration

;=========================

processor 16f84A

include	<p16f84A.inc>
__config	_XT_OSC & _WDT_OFF & _PWRTE_ON & _CP_OFF
;=====================================================
;	constant definitions

; for PIC-to-LCD pin wiring and LCD line addresses ;=====================================================

#define E_line 1		;\|
#define RS_line 2		;\| — from wiring diagram
#define RW_line 3		;\|
; LCD line addresses (from LCD data sheet)
#define LCD_1	0x80	; First LCD line constant
#define LCD_2	0xc0	; Second LCD line constant

;Note: The constants that define the LCD display line

;addresses have the high-order bit set in

;order to facilitate the controller command

;

;=====================================================

;	variables in PIC RAM

;=====================================================

; Reserve 16 bytes for string buffer

cblock 0x0c

strData

endc

LCD Interfacing and Programming			329
; Leave 16 bytes and Continue with local variables
cblock	0x1d		; Start of block
count1		; Counter # 1
count2		; Counter # 2
count3		; Counter # 3
pic_ad		; Storage for start of text area
		; (labeled strData) in PIC RAM
J		; counter J
K		; counter K
index		; Index into text table (also used
		; for auxiliary storage)
store1		; Local temporary storage
store2		; Storage # 2
endc
;=========================================================
;		program
;=========================================================
org	0	; start at address
goto	main
; Space for interrupt handlers
org	0x08
main:
movlw	b’00000000’		; All lines to output
tris	PORTA		; in Port-A
tris	PORTB		; and port B
movlw	b’00000000’		; All outputs ports low
movwf	PORTA
movwf	PORTB
; Wait and initialize HD44780
call	delay_5		; Allow LCD time to initialize
			; itself
call	delay_5
call	initLCD		; Then do forced
initialization
call	delay_5		; Wait again
; Store base address of text buffer in PIC RAM
movlw	0x0c		; Start address for buffer
movwf	pic_ad		; to local variable