; Sample to drive a HD44780 LCD over SPI, using a 74HC595 shift register ; See: https://highfieldtales.wordpress.com/2011/12/04/very-fast-spi-to-parallel-interface-for-netduino/ ; ; PIC 74HC595 HD44780 ; 15 D4 ; 1 D5 ; 2 D6 ; 3 D7 ; 4 RS ; 5 RW ; 6 E ; 7 ; 9 - 12 ; 10 ; CLK 11 ; 12 - 9 ; 13 - GND ; DAT 14 ; ; The SS port resets the shift register, via an inverter list P=16F876A #include p16f876a.inc __CONFIG _CP_ALL & _DEBUG_OFF & _CPD_OFF & _LVP_OFF & _BODEN_ON & _PWRTE_ON & _WDT_OFF & _HS_OSC #define SS_PORT PORTB #define SS PORTB,1 RES_VECT CODE 0x0000 ; processor reset vector GOTO START ; go to beginning of program ; TODO ADD INTERRUPTS HERE IF USED MAIN_PROG CODE ; let linker place main program START banksel TRISC ; Set up pins for SPI bcf TRISC,5 ; Data pin 16 bcf TRISC,3 ; Clock pin 14 bsf TRISC,4 ; Data in clrf TRISB banksel SSPCON ; Set up SPI bcf SSPCON,5 ; Disable SPI movlw b'00010000' movwf SSPCON movlw b'11000000' ; 1 = Input data sampled at end of data output time ; 1 = Transmit occurs on transition from active to Idle clock state movwf SSPSTAT ; bsf SSPCON,4 ; CKP 1 = Idle state for clock is a high level bcf SSPCON,0 ; 0000 = SPI Master mode, clock = FOSC/4 bcf SSPCON,1 bcf SSPCON,2 bcf SSPCON,3 bsf SSPCON,5 ; SSPEN 1 = Enables serial port and configures SCK, SDO, SDI, and SS as serial port pins call init_lcd loop: GOTO loop ; loop forever init_lcd ; Remember to init ports! ; Initialise HD44780 for 4-bits, 2 lines call Delay_100ms ; 100ms, step 1 banksel FLAGS movlw 0 ; Command movwf FLAGS movlw B'00110000' ; initialise module, step 2 call lcd_byte call Delay5ms ; > 4.1ms movlw B'00110000' ; initialise module, step 3 call lcd_byte call Delay100us ; > 100us movlw B'00110000' ; initialise module, step 4 call lcd_byte call Delay100us ; > 100us movlw B'00100000' ; initialise module, step 5 call lcd_byte call Delay100us ; > 100us ;x3 goto x3 ; Step 6, the real function select movlw B'00101100' ; display function (4-bits, 2 lines, 5x10 dots) call lcd_byte call Delay100us ; > 53us movlw B'00001000' ; Step 7, display on/off call lcd_byte call Delay100us ; > 53us movlw B'00000001' ; Step 8, display clear call lcd_byte call Delay5ms ; > 3ms ; |- 0 = Display off, 1 = display on ; |- 0 = 1 line, 1 = 2 line movlw B'00000110' ; Step 9, entry mode. cursor moves right, display not shifted call lcd_byte call Delay100us ; > 53us ; Actual init ends here ; |- 0 = Display off, 1 = Display on ; |- 0 = Cursor off, 1 = Cursor on ; |- 0 = Blink off, 1 = Blink on movlw B'00001111' ; display on, cursor on, blink on call lcd_byte call Delay100us ; > 53us ; Init done, stuff below is just for testing. banksel FLAGS movlw 1 ; Data movwf FLAGS movlw 'A' call lcd_byte movlw 'B' call lcd_byte movlw 'C' call lcd_byte xy movlw 'D' call lcd_byte call Delay_100ms movlw 'E' call lcd_byte return ; Send byte in W to LCD as command or data, depending on FLAGS ; 0 in flags as command or 1 as data lcd_byte banksel D_STO movwf D_STO swapf D_STO,w ; Swap high and low nibbles, result in W andlw b'00001111' ; Mask out call lcd_push_nibble ; Push high nibble banksel D_STO movf D_STO,w ; get byte andlw b'00001111' ; Mask ou call lcd_push_nibble ; Push low nibble call Delay100us ; > 100us delay return ; Push high nibble in w as data or cmd ; Input: Nibble in W, 0 in flags as command or 1 as data lcd_push_nibble ; Push high nibble in w as data or cmd btfsc FLAGS,0 ; flag set=data, set Q4 in that case iorlw b'00010000' ; Not set leave as is iorlw b'10000000' ; Set high bit call send_w_on_spi ; Send nibble, E is still low iorlw b'11000000' ; Set E bit call send_w_on_spi ; Send nibble, E is high andlw b'10111111' ; E -> low call send_w_on_spi ; Send nibble, E is low return send_w_on_spi ;banksel SS_PORT bcf SS ; Assert SS (low) movwf SSPBUF ; begin transmission WAIT btfss PIR1, SSPIF ; send completed? if Yes skip next goto WAIT bcf PIR1, SSPIF ; yes, clear flag ;banksel SS_PORT bsf SS ; Unassert SS (high) return ;----------------------------------------------- ; Delay = 0.0001 seconds ; Clock frequency = 20 MHz ; Actual delay = 0.0001 seconds = 500 cycles ; Error = 0 % Delay100us ;banksel STORE1 ;499 cycles movlw 0xA6 movwf STORE1 Delay100us_0 decfsz STORE1, f goto Delay100us_0 ;1 cycle nop return ;----------------------------------------------- ; Delay = 0.005 seconds ; Clock frequency = 20 MHz ; Actual delay = 0.005 seconds = 25000 cycles ; Error = 0 % Delay5ms ;banksel STORE1 ;24998 cycles movlw 0x87 movwf STORE1 movlw 0x14 movwf STORE2 Delay5ms_0 decfsz STORE1, f goto $+2 decfsz STORE2, f goto Delay5ms_0 ;2 cycles goto $+1 return Delay_100ms ;----------------------------------------------- ; Delay = 0.1 seconds ; Clock frequency = 20 MHz ; Actual delay = 0.1 seconds = 500000 cycles ; Error = 0 % banksel STORE1 ;499994 cycles movlw 0x03 movwf STORE1 movlw 0x18 movwf STORE2 movlw 0x02 movwf STORE3 Delay_100ms_0 decfsz STORE1, f goto $+2 decfsz STORE2, f goto $+2 decfsz STORE3, f goto Delay_100ms_0 ;6 cycles goto $+1 goto $+1 goto $+1 return udata STORE1 res 1 STORE2 res 1 STORE3 res 1 FLAGS res 1 D_STO res 1 END
file: /Techref/io/lcd/dh44780_spi_hc595.htm, 5KB, , updated: 2016/11/9 09:25, local time: 2024/10/4 02:22,
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