#include p16f886.inc
processor p16f886	;not really critical, can set in configure

RESET CODE 0x0000
	goto START

	UDATA;	gpr0
var1 RES 1
var2 RES 2
i2c_address RES 1
i2c_write_data RES 1
i2c_add_search_delay RES 1


	CODE
START:
		CALL SETUP_I2C
		NOP
		CALL FIND_I2C_ADDRESS
		NOP
		CALL LCD_I2C_INF_LOOP
		NOP
		GOTO $

SETUP_I2C:
		;Set SDA (RC4) and SCL (RC3) pins as input
		BANKSEL TRISC
		BSF TRISC, RC3
		BSF TRISC, RC4

		;Enable I2C (bit5), use I2C Master mode (bits 3:0)
		;clock set in this mode FOSC / (4 * (SSPADD+1))
		BANKSEL SSPCON
		MOVLW 0x28
		MOVWF SSPCON
		BANKSEL SSPCON2
		CLRF SSPCON2	;SSPCON2 controls the actual operation. Init to 0
		; SSPADD = (_XTAL_FREQ/(4*feq_K))-1;
		BANKSEL SSPADD
		MOVLW 0x18		;decimal 24 gives 80Khz clock
		MOVWF SSPADD
		BANKSEL SSPSTAT
		CLRF SSPSTAT	;Clear out any status bits

		RETURN

	;wait for I2C to stop being busy
WAIT_I2C:
		;check bit2 of SSPSTAT (in master mode 0 indicates completion)
		BANKSEL SSPSTAT
		BTFSC SSPSTAT,2
		GOTO $-1

		;check the individual operations completion
		;acken, rcen, pen, rsen, sen pg. 180
test_sspcon2:
		BANKSEL SSPCON2
		MOVLW 0x1F
		ANDWF SSPCON2, 0
		BANKSEL STATUS
		BTFSS STATUS,Z			;repeat if status is not 0
		GOTO test_sspcon2

		RETURN

START_I2C:
		;function puts out the start condition after ensuring not busy
		CALL WAIT_I2C
		BANKSEL SSPCON2
		BSF SSPCON2, SEN
		RETURN
STOP_I2C:
		;function puts out the stop condition after ensuring not busy
		CALL WAIT_I2C
		BANKSEL SSPCON2
		BSF SSPCON2, PEN
		RETURN

WRITE_I2C:
		;function writes out to I2C, this is used for both add and data
		;the data should be place ind i2c_write_data
		CALL WAIT_I2C
		BANKSEL i2c_write_data
		MOVF i2c_write_data,0
		BANKSEL SSPBUF
		MOVWF SSPBUF		;place the address or data in SSPBUF for
							;transmission
		RETURN

FIND_I2C_ADDRESS:
		;This function repeatedly checks the I2C lines for presense of
		;the pcf8574 chip and stores the address in i2c_address
		;A retun or 1 indicates success
		;address is 7 bits + LSB r/w`


		MOVLW 0x00					;init W to 0
		BANKSEL i2c_address
		MOVWF i2c_address

addr_search_again:
		CALL START_I2C			;assert start
		BANKSEL i2c_address
		MOVF i2c_address,0
		BANKSEL i2c_write_data
		MOVWF i2c_write_data 	; pass the argument (data to transmit)
		;MOVWF i2c_address		;save the data (actually address)
		CALL WRITE_I2C			;write it out on the bus

		BANKSEL SSPSTAT			;wait for transmission to complete
		BTFSC SSPSTAT,2
		GOTO $-1

		MOVLW 0xFF
		BANKSEL i2c_add_search_delay
		MOVWF i2c_add_search_delay
		MOVLW i2c_add_search_delay
		DECFSZ i2c_add_search_delay,1;decrement W, update W, skip if zero
								;here 0, or 1 both mean the same
		GOTO $-1

		BANKSEL SSPCON2
		BTFSS	SSPCON2, ACKSTAT	;bit ->0 means ack received
		GOTO addr_search_break
		;MOVF i2c_address,0			;restore the address, increment
		;INCFSZ W,0				;on a rollover FF-> 0 break out
		BANKSEL i2c_address
		INCFSZ i2c_address,1	;increment add, resotre to w, skip on rollover
		GOTO addr_search_again

addr_search_break:
		BANKSEL i2c_address
		MOVF i2c_address, 0
		BANKSEL STATUS
		BTFSC	STATUS, Z		;skip if zero flag not set, else return 0
		RETLW 0x00				;0 indicates no response on all address.
		RETLW 0x01

LCD_I2C_INF_LOOP:
		;just an infinite loop writing via I2C to the LCD
		;this is just used to manually program it during ICD
;For the i2c lcd backpack, this is the pin mapping (D0-3 are tied high for 4bit md)
;Bit	7	6	5	4	3	2	1	0
;conn	D7	D6	D5	D4	LED	e	rw	rs

;To use the 1602 in 4 bit mode follow these rules:

;1. Start with the 4 bit config write. The lower nibble is tied low/high. so
;the first one would effectivley be an 8 bit write to set 4 bit mode
;i.e. 88,8c,88 (e -> 0,1,0 with constant data). When it switches modes, it auto
;goes into 2 rows mode dunno why

;2. Now it's in 4 bit mode, send nibbles msb first, strobing e every time
;e.g to set the row count to two, 5x7 char 28,2c,28,88,8c,88

;3. clear the display and we can start using it for displaying letter.
		;CALL START_I2C
		CALL I2C_START
		BANKSEL i2c_address
		MOVF i2c_address, 0
		MOVWF i2c_write_data
		CALL WRITE_I2C	;write address
		NOP
		CALL WAIT_I2C
		;directly modify i2c_write_data address
		NOP
		CALL WRITE_I2C
		NOP
		CALL STOP_I2C
		NOP
		GOTO LCD_I2C_INF_LOOP
		RETURN


END