Файл: Microcontroller Programming. Thi Micro Chip PIC (Julio Sanchez, 2007).pdf
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Analog to Digital and Realtime Clocks |
573 |
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; |
42 microseconds |
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;======================= |
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delay_125 |
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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 |
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return |
; End of delay |
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;=======================
;Procedure to delay
;5 milliseconds ;======================= delay_5:
movlw |
D’41’ |
; Counter = 41 |
|
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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;=============================
;long delay sub-routine
;(for debugging) ;============================= long_delay
movlw |
D’200’ |
; w = 200 decimal |
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movwf |
J |
; J = w |
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jloop: |
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movwf |
K |
; K = w |
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kloop: |
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decfsz |
K,f |
; K = K-1, skip next if zero |
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goto |
kloop |
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decfsz |
J,f |
; J = J-1, skip next if zero |
|
goto |
jloop |
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return |
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;============================= |
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; |
LCD display procedure |
||
574 |
Chapter 16 |
;=============================
;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 |
|
; 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 |
|
; Set up counter for 16 characters |
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movlw |
D’16’ |
; Counter = 16 |
|
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 |
|
getchar: |
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movf |
INDF,w |
; get character from display RAM |
|
; location pointed to by file select |
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; register |
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call |
send8 |
; 4-bit interface routine |
|
; Test for 16 characters displayed |
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decfsz |
count3,f |
; Decrement counter |
|
goto |
nextchar ; Skipped if done |
||
return |
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nextchar: |
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incf |
FSR,f |
; Bump pointer |
|
goto |
getchar |
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;========================
;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 |
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 |
|
swapf |
store1,w ; Swap nibbles in w |
|
call |
merge4 |
|
movwf |
PORTB |
|
call |
pulseE |
; Send data to LCD |
call |
delay_125 |
|
Analog to Digital and Realtime Clocks |
575 |
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 |
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; the original value |
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movwf |
store2 |
; Save result |
in variable |
|
movf |
PORTB,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 |
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;========================
;blank buffer ;========================
;Procedure to store 16 blank characters in PIC RAM
;buffer starting at address stored in the variable
;pic_ad
blank16: |
||
movlw |
D’16’ |
; Setup counter |
movwf |
count1 |
|
movf |
pic_ad,w ; First PIC RAM address |
|
movwf |
FSR |
; Indexed addressing |
movlw |
0x20 |
; ASCII space character |
storeit: |
||
movwf |
INDF |
; Store blank character in PIC |
RAM |
||
; buffer using FSR register |
||
decfsz |
count1,f |
; Done? |
576 |
Chapter 16 |
|
goto |
incfsr |
; no |
return |
; yes |
|
incfsr: |
||
incf |
FSR,f |
; Bump FSR to next buffer |
space |
||
goto |
storeit |
;========================
;Set address register
;to LCD line 1 ;========================
;ON ENTRY:
;Address of LCD line 1 in constant LCD_1
line1:
bcf |
PORTA,E_line |
; E line low |
bcf |
PORTA,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 |
PORTA,RS_line |
; Setup for data |
call |
delay_5 |
; Busy? |
return |
||
;===============================
;first text string procedure ;=============================== storeMS1:
;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
Analog to Digital and Realtime Clocks |
577 |
|
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 |
movwf |
index |
; Store table index in |
variable |
||
goto |
get_msg_char |
; Continue |
endstr1: |
||
return |
||
;Routine for returning message stored in program area
;Message has 10 characters
msg1:
addwf |
PCL,f |
; Access table |
retlw |
‘P’ |
|
retlw |
‘o’ |
|
retlw |
‘t’ |
|
retlw |
‘ ‘ |
|
retlw |
‘R’ |
|
retlw |
‘e’ |
|
retlw |
‘s’ |
|
retlw |
‘i’ |
|
retlw |
‘s’ |
|
retlw |
‘t’ |
|
retlw |
‘:’ |
|
retlw |
0 |
;==============================
;binary to ASCII decimal
;conversion ;==============================
;ON ENTRY:
;w register has binary value in range 0 to 255