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;************************************************
;* 18F_LCD.asm *
;* Microchip Taiwan *
;* Date : Sept. 24 2002 *
;* Version : v1.00 *
;************************************************
;* Contains subroutines to control an external *
;* lcd panel in 4-bit mode. These routines *
;* were designed specifically for the panel on *
;* the PICdemo 2 Plus demo board, but should *
;* work with other LCDs with a HD44780 type *
;* controller. *
;* Routines include: *
;* - InitLCD to initialize the LCD panel *
;* - putcLCD to write a character to LCD *
;* - SendCmd to write a command to LCD *
;* - clrLCD to clear the LCD display *
;* - L1homeLCD to return cursor to line 1 home*
;* - L2homeLCD to return cursor to line 2 home*
;* - PutHexLCD to write a HEX Code to LCD *
;* - Hex2ASCII to convert 4 bits to ASCII Code*
;************************************************
;
list p=18F452
＃i nclude <P18F452.inc>
;
global InitLCD
global putcLCD
global clrLCD
global L1homeLCD
global L2homeLCD
global Send_Cmd
global PutHexLCD
global Hex2ASCII
global Delay_xMS
global Delay_1mS
;
; Defines for I/O ports that provide LCD data & control
; PORTD[0:3]-->DB[4:7]: Higher order 4 lines data bus with bidirectional
; : DB7 can be used as a BUSY flag
; PORTA,1 --> [E] : LCD operation start signal control
; PORTA,2 --> [RW]: LCD Read/Write control
; PORTA,3 --> [RS]: LCD Register Select control
; : "0" for Instrunction register (Write), Busy Flag (Read)
; : "1" for data register (Read/Write)
;
;
LCD_CTRL equ TRISD
LCD_DATA equ PORTD
#define LCD_E_DIR TRISA,1
#define LCD_RW_DIR TRISA,2
#define LCD_RS_DIR TRISA,3
#define LCD_E PORTA,1
#define LCD_RW PORTA,2
#define LCD_RS PORTA,3
; LCD Module commands
CLR_DISP equ b'00000001' ; 1.64mS , Clear display and return cursor to home
Cursor_Home equ b'00000010' ; 1.64mS , Return cursor to home position
ENTRY_DEC equ b'00000100' ; 40uS , Decrement cursor position & No display shift
ENTRY_DEC_S equ b'00000101' ; 40uS , Decrement cursor position & display shift
ENTRY_INC equ b'00000110' ; 40uS , Increment cursor position & No display shift
ENTRY_INC_S equ b'00000111' ; 40uS , Increment cursor position & display shift
DISP_OFF equ b'00001000' ; 40uS , Display off
DISP_ON equ b'00001100' ; 40uS , Display on control
DISP_ON_C equ b'00001110' ; 40uS , Display on, Cursor on
DISP_ON_B equ b'00001111' ; 40uS , Display on, Cursor on, Blink cursor
FUNC_SET equ b'00101000' ; 40uS , 4-bit interface , 2-lines & 5x7 dots
CG_RAM_ADDR equ b'01000000' ; 40uS , Least Significant 6-bit are for CGRAM address
DD_RAM_ADDR equ b'10000000' ; 40uS , Least Significant 7-bit are for DDRAM address
;
; Directs linker to provide 4 variables in GPR memory
UDATA
LCD_Byte RES 1
LCD_Temp RES 1
Count_uS RES 1
Count_mS RES 1
W_BUFR RES 1
Hex_Bfr RES 1
;
LCD_CODE CODE
;*******************************************************************
;* The LCD Module Subroutines *
;* Command sequence for 2 lines of 5x16 characters *
;*******************************************************************
InitLCD
bcf LCD_E ; Clear LCD control line to Zero
bcf LCD_RW
bcf LCD_RS
;
bcf LCD_E_DIR ;configure control lines for Output pin
bcf LCD_RW_DIR
bcf LCD_RS_DIR
;
movlw b'00001110' ; configure AN0 as A/D inut pin
movwf ADCON1
movf LCD_CTRL,W ; get I/O directional settng
andlw 0xF0
movwf LCD_CTRL ; set LCD bus DB[4:7] for output
;
movlw .50 ; Power-On delay 50mS
rcall Delay_xMS
;
movlw b'00000011' ; #1 , Init for 4-bit interface
rcall Send_Low_4bit
;
movlw .10 ; Delay 10 mS
rcall Delay_xMS
;
movlw b'00000011' ; #2 , Fully Initial LCD module
rcall Send_Low_4bit ; Sent '0011' data
rcall Delay_1mS
;
movlw b'00000011' ; #3 , Fully Initial LCD module
rcall Send_Low_4bit ; Sent '0011' data
rcall Delay_1mS
;
movlw b'00000010' ; #4 , Fully Initial LCD module
rcall Send_Low_4bit ; Sent '0010' data
rcall Delay_1mS
;
movlw FUNC_SET ; #5,#6 , Set 4-bit mode , 2 lines & 5 x 7 dots
rcall Send_Cmd
rcall Delay_1mS
;
movlw DISP_ON ; #7,#8 , Turn display on (0x0C)
rcall Send_Cmd
rcall Delay_1mS
;
movlw CLR_DISP ; #9,#10 , Clear LCD Screen
rcall Send_Cmd
movlw .5 ; Delay 5mS for Clear LCD Command execution
rcall Delay_xMS
;
movlw ENTRY_INC ; #11,#12 , Configure cursor movement
rcall Send_Cmd
rcall Delay_1mS
;
movlw DD_RAM_ADDR ; Set writes for display memory
rcall Send_Cmd
rcall Delay_1mS
;
return
;
;*******************************************************************
;*SendChar - Sends character to LCD *
;*This routine splits the character into the upper and lower *
;*nibbles and sends them to the LCD, upper nibble first. *
;*******************************************************************
putcLCD
movwf LCD_Byte ; Save WREG in Byte variable
rcall Send_High_LCD ; Send upper nibble first
movf LCD_Byte,W
rcall Send_Low_LCD ; Send lower nibble data
rcall Delay_100uS
return
;
Send_High_LCD
swapf WREG,W ; swap high/low nibble
Send_Low_LCD
bcf LCD_RW ; set LCD Write Mode
andlw 0x0F ; Clear high nibble
movwf LCD_Temp
movf LCD_DATA,W ; Read back PORT
andlw 0xF0 ; keep data for PORTD[4:7]
iorwf LCD_Temp,W
movwf LCD_DATA ; Write data to LCD bus for low nibble bus DB[4:7]
bsf LCD_RS ; Set for data input
nop
bsf LCD_E ; Clock nibble into LCD
nop
bcf LCD_E
return
;
;*********************************************************************
;* To put the HEX value to LCD Display ,,
;* High nibble first than Low nibble
;* Input : W Reg.
;*********************************************************************
PutHexLCD
movwf W_BUFR ; Save W Register !!
swapf W_BUFR,W ; High nibble first !!
rcall Hex2ASCII
rcall putcLCD
;
movf W_BUFR,W
rcall Hex2ASCII
rcall putcLCD
return
;
;******************************************************************
;* Convert a low nibble to ASCII code
;* Input : W Reg.
;* Output: W Reg.
;******************************************************************
Hex2ASCII
andlw 0x0f ; Mask Bit 4 to 7
movwf Hex_Bfr
sublw .09
btfsc STATUS,C ; If W less than A (C=1) --> only add 30h
bra _Add_W_30
_Add_W_37 movlw 0x37
bra _Hex_cont
_Add_W_30 movlw 0x30
_Hex_cont addwf Hex_Bfr,W ; The correct ASCII code for this char !!
return
;
;*******************************************************************
;* SendCmd - Sends command to LCD *
;* This routine splits the command into the upper and lower *
;* nibbles and sends them to the LCD, upper nibble first. *
;*******************************************************************
; _ ______________________________
; RS _>--<______________________________
; _____
; RW \_____________________________
; __________________
; E ____________/ \___
; _____________ ______
; DB _____________>--------------<______
;
Send_Cmd
movwf LCD_Byte ; Save WREG in Byte variable
rcall Send_High_4bit ; Send upper nibble first
movf LCD_Byte,W
rcall Send_Low_4bit ; Send lower nibble data
rcall Delay_100uS
return
;
Send_High_4bit
swapf WREG,W ; swap high/low nibble
Send_Low_4bit
bcf LCD_RW ; set LCD Write Mode
andlw 0x0F ; Clear high nibble
movwf LCD_Temp
movf LCD_DATA,W ; Read back PORT
andlw 0xF0 ; keep data for PORTD[4:7]
iorwf LCD_Temp,W
movwf LCD_DATA ; Write data to LCD bus for low nibble bus DB[4:7]
bcf LCD_RS ; Clear for command inut
nop
bsf LCD_E ; Clock nibble into LCD
nop
bcf LCD_E
return
;
;*******************************************************************
;* clrLCD - Clear the contents of the LCD *
;*******************************************************************
clrLCD
movlw CLR_DISP ; Clear LCD screen
rcall Send_Cmd
movlw .5 ; Delay 5mS for Clear LCD Command execution
bra Delay_xMS
;
;*******************************************************************
;* L1homeLCD - Moves the cursor to home position on Line 1 *
;*******************************************************************
L1homeLCD
movlw DD_RAM_ADDR|0x00 ; Send command to move cursor to
rcall Send_Cmd ; home position on line 1
bra Delay_100uS
;
;*******************************************************************
;* L2homeLCD - Moves the cursor to home position on Line 2 *
;*******************************************************************
L2homeLCD
movlw DD_RAM_ADDR|0x40 ; Send command to move cursor to
rcall Send_Cmd ; home position on line 2
bra Delay_100uS
;
;*******************************************************************
;* Delay - 1mS base delay *
;* input : W Reg. *
;* *
;*******************************************************************
Delay_xMS
movwf Count_mS
;
_D_1mS call Delay_1mS
decfsz Count_mS,F
goto _D_1mS
return
;
;*******************************************************************
;* Delay_1mS - Generic LCD delay (1.00mS @ 4MHz) *
;* Delay_100uS - Generic LCD delay 100us @ 4Mhz * *
;*******************************************************************
Delay_1mS
movlw .248 ; Load 1mS Dealy Value
bra Delay_uS
;
Delay_100uS
movlw .25 ; Load delay 100uS value
Delay_uS movwf Count_uS ; Save to Count2
_D_uS nop
decfsz Count_uS,F ; Count2 - 1 = 0 ?
bra _D_uS
return
;
END
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