Файл: Microcontroller Programming. Thi Micro Chip PIC (Julio Sanchez, 2007).pdf

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716	Appendix D

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

;Procedure to delay

;5 milliseconds ;======================= delay_5:

		movlw	.105		; Counter = 105 cycles
		movwf	count2		; Store in variable
delay
		call	delay_125		; Delay
		decfsz	count2,f		; 40 times = 5 milliseconds
		goto	delay
		return			; End of delay
;========================
;		pulse E line
;========================
pulseE
		bsf	PORTE,E_line		; Pulse E line
		nop
		bcf	PORTE,E_line
		return
;=============================
;	long delay sub-routine
;=============================
long_delay
			movlw	D'200'	; w delay count
			movwf	J	; J = w
jloop:		movwf	K		; K = w
kloop:		decfsz	K,f		; K = K-1, skip next if zero
			goto	kloop
			decfsz	J,f	; J = J-1, skip next if zero
			goto	jloop
			return

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

;send 2 nibbles in

;4-bit mode ;========================

;Procedure to send two 4-bit values to port B lines

;7, 6, 5, and 4. High-order nibble is sent first

;ON ENTRY:

;w register holds 8-bit value to send

send8:

movwf	store1	; Save		original value
call	merge4	; Merge with port B
; Now w has merged byte
movwf	PORTD	;	w to	port	D
call	pulseE	;	Send	data	to LCD

; High nibble is sent

Supplementary Programs			717
movf	store1,w	; Recover byte	into w
swapf	store1,w	; Swap nibbles	in w
call	merge4
movwf	PORTD
call	pulseE	; Send data to	LCD
call	delay_125
return

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

;merge bits ;==========================

;Routine to merge the 4 high-order bits of the

;value to send with the contents of port B

;so as to preserve the 4 low-bits in port B

;Logic:

;AND value with 1111 0000 mask

;AND port B with 0000 1111 mask

;Now low nibble in value and high nibble in

;port B are all 0 bits:

;value = vvvv 0000

;port B = 0000 bbbb

;OR value and port B resulting in:

;

vvvv bbbb

;ON ENTRY:

;w contain value bits

;ON EXIT:

;w contains merged bits

merge4:

andlw	b'11110000'	; ANDing with	0 clears the
		; bit. ANDing	with 1 preserves
		; the original value
movwf	store2	; Save result	in variable
movf	PORTD,w	; port B to w	register
andlw	b'00001111' ; Clear high nibble in port b
		; and preserve low nibble
iorwf	store2,w ; OR two operands in w
return

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

;Set address register

;to LCD line 2 ;==========================

;ON ENTRY:

;Address of LCD line 2 in constant LCD_2

line2:

bcf	PORTE,E_line	; E line low
bcf	PORTE,RS_line	; RS line low, setup for
		;	control
call	delay_5	;	Busy?

; Set to second display line

718		Appendix D
movlw	LCD_2	; Address with high-bit set
call	send8
; Set RS line for data
bsf	PORTE,RS_line	; RS = 1 for data
call	delay_5	; Busy?
return

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

;Set address register

;to LCD line 1 ;==========================

;ON ENTRY:

;Address of LCD line 1 in constant LCD_1

line1:

bcf	PORTE,E_line	; E line low
bcf	PORTE,RS_line	; RS line low, set up for
		; control
call	delay_5	; busy?
; Set to second display line
movlw	LCD_1	; Address and command bit
call	send8	; 4-bit routine
; Set RS line for data
bsf	PORTE,RS_line	; Setup for data
call	delay_5	; Busy?
return

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

;scroll to LCD line 2 ;==========================

;Procedure to count the number of characters displayed on

;each LCD line. If the number reaches the value in the

;constant LCDlimit, then display is scrolled to the second

;LCD line. If at the end of the second line, then LCD is

;reset to the first line.

LCDscroll:
incf	LCDcount,f	; Bump counter
; Test for line limit
movf	LCDcount,w
sublw	LCDlimit	; Count minus limit
btfss	STATUS,Z	; Is count - limit = 0
goto	scrollExit	; Go if not at end of line

;At this point the end of the LCD line was reached

;Test if this is also the end of the second line

movf	LCDline,w
sublw	0x01	; Is it line 1?
btfsc	STATUS,Z	; Is LCDline minus 1 = 0?
goto	line2End	; Go if end of second line
; At this point it is the end of the top LCD line
call	line2	; Scroll to second line

Supplementary Programs		719
clrf	LCDcount	; Reset counter
incf	LCDline,f	; Bump line counter
goto	scrollExit
; End of second LCD line
line2End:
call	initLCD	; Reset
clrf	LCDcount	; Clear counters
clrf	LCDline
call	line1	; Display to first line
scrollExit:
return

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

;LCD display procedure ;=============================

;Sends 20 characters from PIC buffer with address stored

;in variable bufAdd to LCD line previously selected display20:

call	delay_5		; Make sure not busy
; Set up for data
bcf	PORTA,E_line		; E line low
bsf	PORTA,RS_line		; RS line high for data
; Set up counter for 20 characters
movlw	D'20'
movwf	count3
; Get display address from local variable bufAdd
movf	bufAdd,w	; First display RAM address to W
movwf	FSR		; W to FSR
getchar
movf	INDF,w	; get character from display RAM
		; location pointed to by file select
		; register
call	send8	; 4-bit interface routine
; Test for 20 characters displayed
decfsz	count3,f		; Decrement counter
goto	nextchar		; Skipped if done
return
nextchar:
incf	FSR,f		; Bump pointer
goto	getchar

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

;first text string procedure ;=============================== storeMS1:

;Procedure to store in PIC RAM buffer the message

;contained in the code area labeled msg1

;ON ENTRY:

720	Appendix D

;variable bufAdd 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	bufAdd,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
movwf	index	; Store table index in variable
goto	get_msg_char		; Continue
endstr1:
return