Файл: Microcontroller Programming. Thi Micro Chip PIC (Julio Sanchez, 2007).pdf
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330 |
Chapter 13 |
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movlw |
d’3’ |
; Offset into buffer |
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call |
storeMSU |
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; Set DDRAM address to start of first line |
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call |
line1 |
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; Call procedure to display 16 characters in LCD |
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call |
display16 |
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;======================== |
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; |
second LCD line |
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;======================== |
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call |
delay_5 |
; Wait for termination |
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call |
blank16 |
; Blank buffer |
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;Call procedure to store ASCII characters for message
;in text buffer
movlw |
d’1’ |
; Offset into buffer |
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call |
storeUniv |
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call |
line2 |
; DDRAM address of LCD line 2 |
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call |
display16 |
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;======================= |
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; |
done! |
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;======================= |
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loopHere: |
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goto |
loopHere |
;done |
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;============================================================ ; initialize LCD for 4-bit mode ;============================================================ initLCD:
;Initialization for Densitron LCD module as follows:
;4-bit interface
;2 display lines of 16 characters each
;cursor on
;left-to-right increment
;cursor shift right
;no display shift
;=======================| |
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; |
set command mode |
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;=======================| |
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bcf |
PORTA,E_line |
; E line low |
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bcf |
PORTA,RS_line |
; RS line low |
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bcf |
PORTA,RW_line |
; Write mode |
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call |
delay_125 |
; delay 125 |
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microseconds |
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;***********************| |
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; |
FUNCTION SET |
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;***********************| |
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movlw |
0x28 |
; 0 0 1 0 1 0 0 0 (FUNCTION SET) |
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; |
| | | |__ font select: |
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; |
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1 = 5x10 in 1/8 or 1/11 |
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LCD Interfacing and Programming |
331 |
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; |
| | | |
0 = 1/16 dc |
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; |
| | |___ Duty cycle select |
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; |
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0 = 1/8 or 1/11 |
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; |
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1 = 1/16 |
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; |
| |___ Interface width |
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; |
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0 = 4 bits |
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; |
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1 = 8 bits |
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; |
|___ FUNCTION SET COMMAND |
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call |
send8 |
; 4-bit send routine |
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; Set 4-bit mode command must be repeated |
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movlw |
0x28 |
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call |
send8 |
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;***********************| |
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; DISPLAY AND CURSOR ON | |
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;***********************| |
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movlw |
0x0e |
; 0 0 0 0 1 1 1 0 (DISPLAY ON/OFF) |
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; |
| | | |___ Blink character |
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; |
| | | |
1 = on, 0 = off |
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; |
| | |___ Cursor on/off |
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; |
| | |
1 = on, 0 = off |
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; |
| |____ Display on/off |
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; |
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1 = on, 0 = off |
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; |
|____ COMMAND BIT |
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call |
send8 |
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;***********************| |
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; |
set entry mode |
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;***********************| |
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movlw |
0x06 |
; 0 0 0 0 0 1 1 0 (ENTRY MODE SET) |
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; |
| | |___ display shift |
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; |
| | |
1 = shift |
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; |
| | |
0 = no shift |
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; |
| |____ increment mode |
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; |
| |
1 = left-to-right |
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; |
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0 = right-to-left |
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; |
|___ COMMAND BIT |
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call |
send8 |
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;***********************| |
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; cursor/display shift |
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;***********************| |
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movlw |
0x14 |
; 0 0 0 1 0 1 0 0 (CURSOR/DISPLAY |
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; |
| | | | | SHIFT) |
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; |
| | | |_|___ don’t care |
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; |
| |_|__ cursor/display shift |
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; |
| |
00 = cursor shift left |
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; |
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01 = cursor shift right |
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; |
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10 = cursor and display |
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332 |
Chapter 13 |
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; |
| |
shifted left |
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; |
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11 = cursor and display |
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; |
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shifted right |
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; |
|___ COMMAND BIT |
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call |
send8 |
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;***********************| |
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; |
clear display |
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;***********************| |
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movlw |
0x01 |
; 0 0 0 0 |
0 0 0 1 (CLEAR DISPLAY) |
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; |
|___ COMMAND BIT |
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call |
send8 |
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; Per documentation |
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call |
delay_5 |
; Test for busy |
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return |
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;=======================
;Procedure to delay
;42 microseconds ;======================= delay_125
movlw |
D’42’ |
; Repeat 42 machine cycles |
movwf |
count1 |
; Store value in counter |
repeat |
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decfsz |
count1,f |
; Decrement counter |
goto |
repeat |
; Continue if not 0 |
return |
; End of delay |
;=======================
;Procedure to delay
;5 milliseconds ;======================= delay_5:
movlw |
D’41’ |
; Counter = 41 |
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movwf |
count2 |
; Store in variable |
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delay: |
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call |
delay_125 |
; Delay |
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decfsz |
count2,f |
; 40 times = 5 milliseconds |
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goto |
delay |
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return |
; End of delay |
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;======================== |
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; |
pulse E line |
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;======================== |
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pulseE |
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bsf |
PORTA,E_line |
; Pulse E line |
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nop |
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bcf |
PORTA,E_line |
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return |
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LCD Interfacing and Programming |
333 |
;=============================
;long delay sub-routine
;(for debugging) ;============================= long_delay:
movlw |
D’200’ |
; w = 200 decimal |
movwf |
J |
; J = w |
jloop: |
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movwf |
K |
; K = w |
kloop: |
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decfsz |
K,f |
; K = K-1, skip next if zero |
goto |
kloop |
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decfsz |
J,f |
; J = J-1, skip next if zero |
goto |
jloop |
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return |
;=============================
;LCD display procedure ;=============================
;Sends 16 characters from PIC buffer with address stored
;in variable pic_ad to LCD line previously selected display16
call |
delay_5 |
; Make sure not busy |
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; Set up for data |
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bcf |
PORTA,E_line |
; E line low |
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bsf |
PORTA,RS_line |
; RS line high for data |
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; Set up counter for 16 characters |
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movlw |
D’16’ |
; Counter = 16 |
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movwf |
count3 |
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; Get display address from local variable pic_ad |
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movf |
pic_ad,w ; First display RAM address to W |
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movwf |
FSR |
; W to FSR |
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getchar: |
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movf |
INDF,w |
; get character from display RAM |
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; location pointed to by file select |
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; register |
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call |
send8 |
; 4-bit interface routine |
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; Test for 16 characters displayed |
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decfsz |
count3,f |
; Decrement counter |
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goto |
nextchar |
; Skipped if done |
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return |
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nextchar: |
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incf |
FSR,f |
; Bump pointer |
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goto |
getchar |
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;========================
;send 2 nibbles in
;4-bit mode ;========================
334 |
Chapter 13 |
;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 |
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; Now w has merged byte |
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movwf |
PORTB |
; w to |
port B |
call |
pulseE |
; Send |
data to LCD |
; High nibble is sent |
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movf |
store1,w |
; Recover byte into w |
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swapf |
store1,w |
; Swap |
nibbles in w |
call |
merge4 |
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movwf |
PORTB |
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call |
pulseE |
; Send |
data to LCD |
call |
delay_125 |
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return |
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;=================
;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 |
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; bit. ANDing |
with 1 preserves |
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; the original value |
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movwf |
store2 |
; |
Save |
result |
in variable |
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movf |
PORTB,w |
; |
port |
B |
to w |
register |
andlw |
b’00001111’ |
Clear high nibble |
in port b |
; and preserve low |
nibble |
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iorwf |
store2,w ; OR two operands in w |
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return |
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