WebSVN – group.electronics – Blame – /PIC_Projects/PIC_Tutorial/Part01-I2C/master00_read_write.asm

Rev	Author	Line No.	Line
6	pfowler	1	`list p=16F84A`
		2	`include "p16F84a.inc"`
		3
		4	`;***** CONFIGURATION`
		5	`__CONFIG _PWRTE_ON & _HS_OSC & _WDT_OFF`
		6
		7	`; pin assignments`
		8	`#define SDA 0 ; Pin 0`
		9	`#define SCL 1 ; Pin 1`
		10	`#define TRIS_SDA TRISB,SDA`
		11	`#define TRIS_SCL TRISB,SCL`
		12	`#define I2C_SDA PORTB,SDA`
		13	`#define I2C_SCL PORTB,SCL`
		14	`#define LED PORTB,2`
		15
		16	`#define I2C_SLAVE1 0x27`
		17	`#define I2C_SLAVE2 0x26`
		18
		19	`CBLOCK 0CH`
		20
		21	`_I ; Loop counter`
		22	`byte_send ; Byte to send to i2c`
		23	`byte_read ; Byte read from i2c`
		24	`byte_temp ; Store byte while address send`
		25	`i2c_addr ; Address to read/write`
		26	`i2c_ret ; I2C Return Value`
		27
		28	`dly_loop1 ; Loops for delays`
		29	`dly_loop2`
		30	`ENDC`
		31
		32	`ORG 0`
		33	`goto start ; jump over to main routine`
		34
		35	`;***** Initialisation`
		36	`start`
		37	`; configure ports`
		38	`clrw ; configure PORTB as all outputs`
		39	`tris PORTB`
		40	`clrf PORTB`
		41	`movlw b'00001011' ; RA0 - Input - Toggle SW, Mode Select`
		42	`; RA1 - Input - Pulse SW, Record`
		43	`; RA2 - Output - LED, Mode`
		44	`; RA3 - Input - Switch, Reset`
		45	`tris PORTA`
		46
		47	`clrf byte_send`
		48	`clrf byte_read`
		49
		50	`;***** Main loop`
		51	`main_loop`
		52	`bsf LED`
		53	`call ReadByte ; Read byte from SLAVE2`
		54	`bcf LED`
		55
		56	`movfw byte_read ; Copy the byte read`
		57	`;movlw b'10101010'`
		58	`movwf byte_send ; into the byte to send`
		59
		60	`call Delay_Short`
		61
		62	`bsf LED`
		63	`call SendByte ; Send byte to SLAVE1`
		64	`bcf LED`
		65
		66	`call Delay_Long`
		67	`goto main_loop`
		68
		69	`ReadByte`
		70	`movlw I2C_SLAVE2 ; Address of Slave2`
		71	`movwf i2c_addr`
		72	`bsf STATUS,C ; Set mode to read`
		73	`call I2C_Start ; Send the address with mode`
		74	`call ReadAck`
		75	`;movf i2c_ret`
		76	`;btfss STATUS,Z`
		77	`;goto SendErr`
		78	`call I2C_Read ; Read byte into byte_read`
		79	`call ReadAck`
		80
		81	`call I2C_End`
		82
		83	`return`
		84
		85	`SendByte`
		86	`movfw byte_send ; Save the byte while sending address`
		87	`movwf byte_temp`
		88	`movlw I2C_SLAVE1 ; 7-bit address of dev`
		89	`movwf i2c_addr ; Set it in the address`
		90	`bcf STATUS,C ; Use Write mode ('0')`
		91	`call I2C_Start ; Start a transmission`
		92	`call ReadAck ; Wait for Ack from slave`
		93	`;movf i2c_ret ; Check return value`
		94	`;btfss STATUS,Z ; Goto SendEnd on NACK`
		95	`;goto SendErr`
		96	`movfw byte_temp`
		97	`movwf byte_send`
		98	`;movfw byte_send ; Copy byte to write (counter) to w`
		99	`call I2C_Write ; Write the byte to the line`
		100	`call ReadAck ; Should read byte from bus here`
		101	`; checking that its a Nack`
		102
		103	`call I2C_End ; End the packet`
		104
		105	`return`
		106
		107	`SendErr`
		108	`call I2C_End`
		109
		110	`return`
		111
		112
		113	`I2C_Start`
		114	`rlf i2c_addr,f ; Attach mode (STATUS,C) to 1st bit`
		115	`call Start ; Start the Trans`
		116	`movfw i2c_addr`
		117	`movwf byte_send ; Send the complete address`
		118	`call I2C_Write ; Write byte to port`
		119	`return`
		120
		121	`I2C_End`
		122	`call Stop`
		123	`return`
		124
		125	`I2C_Write`
		126	`;movwf byte_send`
		127	`movlw .8 ; 8 bits to send`
		128	`movwf _I`
		129	`_WriteBit`
		130	`rlf byte_send,f ; Move highest bit to C`
		131	`btfss STATUS,C ; If 'C' is clear`
		132	`call SDA_Low ; -> Set data low`
		133	`btfsc STATUS,C ; If 'C' is set`
		134	`call SDA_High ; -> Set data high`
		135
		136	`call SCL_Pulse`
		137
		138	`decfsz _I,f ; Decrement counter, if not clear`
		139	`goto _WriteBit ; -> Send next bit`
		140	`call SDA_Low ; Set low to allow slave to write`
		141	`return`
		142
		143	`I2C_Read`
		144	`movlw .8 ; 8 bits to read`
		145	`movwf _I`
		146	`clrf byte_read ; Clear the read byte`
		147	`bcf STATUS,C`
		148	`call SDA_High ; Set high so slave can write`
		149	`_ReadBit`
		150	`call SCL_High ; Pull Clock high, bit should arrive`
		151	`;btfss I2C_SDA ; If sda is clear`
		152	`bcf STATUS,C ; -> Set status 0`
		153	`btfsc I2C_SDA ; If sda is set`
		154	`bsf STATUS,C`
		155	`call SCL_Low ; Send the clock low`
		156
		157	`rlf byte_read,f ; Move highest bit to C`
		158
		159	`decfsz _I,f ; Decrement counter, if not clear`
		160	`goto _ReadBit ; -> Send next bit`
		161	`;call SDA_Low ; Set low to allow slave to write`
		162	`return`
		163
		164	`Nack ; Clock a high SDA`
		165	`call SDA_High`
		166	`call SCL_Pulse`
		167	`return`
		168
		169	`Ack ; Clock a high SDA`
		170	`call SDA_Low`
		171	`call SCL_Pulse`
		172	`return`
		173
		174	`ReadAck`
		175	`call SDA_High ; SDA high to allow slave to write`
		176	`call SCL_High`
		177	`clrf i2c_ret`
		178	`btfsc I2C_SDA`
		179	`bsf i2c_ret,0`
		180	`call SCL_Low`
		181	`return`
		182
		183	`Start`
		184	`call SDA_High`
		185	`call SCL_High`
		186	`call SDA_Low`
		187	`call SCL_Low`
		188	`return`
		189
		190	`Stop ; Bring SDA high while Clock high`
		191	`call SCL_Low`
		192	`call SDA_Low`
		193	`call SCL_High`
		194	`call SDA_High`
		195	`return`
		196
		197	`SCL_Pulse`
		198	`call SCL_High`
		199	`call SCL_Low`
		200	`return`
		201
		202	`SDA_High`
		203	`bsf STATUS,RP0 ; Bank 1`
		204	`bsf TRIS_SDA ; Make SDA pin input`
		205	`bcf STATUS,RP0 ; Back to bank 0`
		206	`call Delay_Short`
		207	`return`
		208
		209	`SDA_Low`
		210	`bcf I2C_SDA`
		211	`bsf STATUS,RP0`
		212	`bcf TRIS_SDA ; Make SDA pin output`
		213	`bcf STATUS,RP0`
		214	`call Delay_Short`
		215	`return`
		216
		217	`SCL_High`
		218	`bsf STATUS,RP0 ; Bank 1`
		219	`bsf TRIS_SCL ; Make SDA pin input`
		220	`bcf STATUS,RP0 ; Back to bank 0`
		221	`call Delay_Short`
		222	`return`
		223
		224	`SCL_Low`
		225	`bcf I2C_SCL`
		226	`bsf STATUS,RP0`
		227	`bcf TRIS_SCL ; Make SDA pin output`
		228	`bcf STATUS,RP0`
		229	`call Delay_Short`
		230	`return`
		231
		232	`Delay_Short ; 25us delay`
		233	`movlw .5`
		234	`movwf dly_loop2`
		235	`Delay_Short_1`
		236	`nop`
		237	`decfsz dly_loop2,f`
		238	`goto Delay_Short_1`
		239	`return`
		240
		241	`Delay_Long`
		242	`movlw .250 ; 250ms delay`
		243	`movwf dly_loop1`
		244	`Outer`
		245	`movlw .110 ; Close to 1ms when set to .110`
		246	`movwf dly_loop2`
		247	`Inner`
		248	`nop`
		249	`nop`
		250	`nop`
		251	`nop`
		252	`nop`
		253	`nop`
		254	`decfsz dly_loop2,f`
		255	`goto Inner`
		256	`decfsz dly_loop1,f`
		257	`goto Outer`
		258	`return`
		259
		260	`END`
		261

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