; ****************************************************************************** ; Virtual Peripheral: I2C Subroutines ; ; Length: 133 bytes (total) ; Authors: Chip Gracey, President, Parallax Inc. ; modified by Craig Webb, Consultant to Scenix Semiconductor, Inc. ; Written: 97/03/10 to 98/6/03 ; ;****************************************************************************** ; ;****** Assembler directives ; ; uses: SX28AC, 2 pages of program memory, 8 banks of RAM, high speed osc. ; operating in turbo mode, with 8-level stack & extended option reg. ; DEVICE pins28,pages2,banks8,oschs DEVICE turbo,stackx,optionx ID 'I2C' ;program ID label RESET reset_entry ;set reset/boot address ; ;******************************* Program Variables *************************** ; ; Port Assignment: Bit variables ; scl EQU RA.0 ;I2C clock sda EQU RA.1 ;I2C data I/O ; ; ;****** Register definitions (bank 0) ; org 8 ;start of program registers main = $ ;main bank ; temp ds 1 ;temporary storage byte ds 1 ;temporary UART/I2C shift reg. flags DS 1 ;program flags register ; seq_flag EQU flags.1 ;I2C: R/W mode (if sequential=1) got_ack EQU flags.2 ; if we got ack signal ; org 90H ;bank4 variables I2C EQU $ ;I2C bank ; data DS 1 ;data byte from/for R/W address DS 1 ;byte address count DS 1 ;bit count for R/W delay DS 1 ;timing delay for write cycle byte_count DS 1 ;number of bytes in R/W num_bytes DS 1 ;number of byte to view at once save_addr DS 1 ;backup location for address ; in_bit EQU byte.0 ;bit to receive on I2C out_bit EQU byte.7 ;bit to transmit on I2C ; control_r = 10100001b ;control byte: read E2PROM control_w = 10100000b ;control byte: write E2PROM portsetup_r = 00000110b ;Port A config: read bit portsetup_w = 00000100b ;Port A config: write bit eeprom_size = 128 ;storage space of EEPROM ; t_all = 31 ;bit cycle delay (62=5 usec) ; ; ORG 0h ;Program Start adress ; ;******************************** I2C Subroutines ***************************** ; ; These routines write/read data to/from the 24LCxx EEPROM at a rate of approx. ; 200kHz. For faster* reads (up to 400 kHz max), read, write, start amd stop ; bit cycles and time between each bus access must be individually tailored ; using the CALL Bus_delay:custom entry point with appropriate values in the W ; register - in turbo mode: delay[usec] = 1/xtal[MHz] * (6 + 4 * (W-1)). ; Acknowledge polling is used to reduce delays between successive operations ; where the first of the two is a write operation. In this case, the speed ; is limited by the EEPROM's storage time. ; ;****** Subroutine(s) : Write to I2C EEPROM ; These routines write a byte to the 24LCxxB EEPROM. Before calling this ; subroutine, the address and data registers should be loaded accordingly. The ; sequential mode flag should be clear for normal byte writing operation. ; To write in sequential/page mode, please see application note. ; ; Input variable(s) : data, address, seq_flag ; Output variable(s) : none ; Variable(s) affected : byte, temp, count, delay ; Flag(s) affected : none ; Timing (turbo) : approx. 200 Kbps write rate ; : approx. 10 msec between successive writes ; I2C_write CALL Set_address ;write address to slave :page_mode MOV W,data ;get byte to be sent CALL Write_byte ;Send data byte JB seq_flag,:done ;is this a page write? CALL Send_stop ;no, signal stop condition :done RETP ;leave and fix page bits ; Set_address CALL Send_start ;send start bit MOV W,#control_w ;get write control byte CALL Write_byte ;Write it & use ack polling JNB got_ack,Set_address ; until EEPROM ready MOV W,address ;get EEPROM address pointer CALL Write_byte ; and send it RETP ;leave and fix page bits ; Write_byte MOV byte,W ;store byte to send MOV count,#8 ;set up to write 8 bits :next_bit CALL Write_bit ;write next bit RL byte ;shift over to next bit DJNZ count,:next_bit ;whole byte written yet? CALL Read_bit ;yes, get acknowledge bit SETB got_ack ;assume we got it SNB in_bit ;did we get ack (low=yes)? CLRB got_ack ;if not, flag it ; ; to use the LED as a 'no_ack' signal, the ':toggle_led' line in the interrupt ; section must be commented out, and the next 3 instructions uncommented. ; CLRB led_pin ;default: LED off ; SNB in_bit ;did we get ack (low=yes)? ; SETB led_pin ; if not, flag it with LED ; RETP ;leave and fix page bits ; Write_bit MOVB sda,out_bit ;put tx bit on data line MOV !ra,#portsetup_w ;set Port A up to write JMP :delay1 ;100ns data setup delay :delay1 JMP :delay2 ; (note: 250ns at low power) :delay2 SETB scl ;flip I2C clock to high ; MOV W,#t_high ;get write cycle timing* CALL Bus_delay ;do delay while bus settles CLRB scl ;return I2C clock low MOV !ra,#portsetup_r ;set sda->input in case ack ; MOV W,#t_low ;get clock=low cycle timing* CALL Bus_delay ;allow for clock=low cycle RETP ;leave and fix page bits ; Send_start SETB sda ;pull data line high MOV !ra,#portsetup_w ;setup I2C to write bit JMP :delay1 ;100ns data setup delay :delay1 JMP :delay2 ; (note: 250ns at low power) :delay2 SETB scl ;pull I2C clock high ; MOV W,#t_su_sta ;get setup cycle timing* CALL Bus_delay ;allow start setup time :new CLRB sda ;data line goes high->low ; MOV W,#t_hd_sta ;get start hold cycle timing* CALL Bus_delay ;allow start hold time CLRB scl ;pull I2C clock low ; MOV W,#t_buf ;get bus=free cycle timing* CALL Bus_delay ;pause before next function RETP ;leave and fix page bits ; Send_stop CLRB sda ;pull data line low MOV !ra,#portsetup_w ;setup I2C to write bit JMP :delay1 ;100ns data setup delay :delay1 JMP :delay2 ; (note: 250ns at low power) :delay2 SETB scl ;pull I2C clock high ; MOV W,#t_su_sto ;get setup cycle timing* CALL Bus_delay ;allow stop setup time SETB sda ;data line goes low->high ; MOV W,#t_low ;get stop cycle timing* CALL Bus_delay ;allow start/stop hold time RETP ;leave and fix page bits ; Bus_delay MOV W,#t_all ;get timing for delay loop :custom MOV temp,W ;save it :loop DJNZ temp,:loop ;do delay RETP ;leave and fix page bits ; ;****** Subroutine(s) : Read from I2C EEPROM ; These routines read a byte from a 24LCXXB E2PROM either from a new address ; (random access mode), from the current address in the EEPROM's internal ; address pointer (CALL Read_byte:current), or as a sequential read. In either ; the random access or current address mode, seq_flag should be clear. Please ; refer to the application note on how to access the sequential read mode. ; ; Input variable(s) : address, seq_flag ; Output variable(s) : data ; Variable(s) affected : byte, temp, count, delay ; Flag(s) affected : none ; Timing (turbo) : reads at approx. 200Kbps ; I2C_read CALL Set_address ;write address to slave :current CALL Send_start ;signal start of read MOV W,#control_r ; get read control byte CALL Write_byte ; and send it :sequential MOV count,#8 ;set up for 8 bits CLR byte ;zero result holder :next_bit RL byte ;shift result for next bit CALL Read_bit ;get next bit DJNZ count,:next_bit ;got whole byte yet? MOV data,byte ;yes, store what was read SB seq_flag ;is this a sequential read? :non_seq JMP Send_stop ; no, signal stop & exit CLRB out_bit ; yes, setup acknowledge bit CALL Write_bit ; and send it RETP ;leave and fix page bits ; Read_bit CLRB in_bit ;assume input bit low MOV !ra,#portsetup_r ;set Port A up to read SETB scl ;flip I2C clock to high ; MOV W,#t_high ;get read cycle timing* CALL Bus_delay ;Go do delay SNB sda ;is data line high? SETB in_bit ;yes, switch input bit high CLRB scl ;return I2C clock low ; MOV W,#t_buf ;get bus=free cycle timing* CALL Bus_delay ;Go do delay RETP ;leave and fix page bits ; ; ***** High level functions: Store byte & Erase ; Store_W BANK I2C ;switch to EEPROM bank MOV data,W ;save incoming value CALL I2C_Write ;store it in EEPROM INC address ;move to next address INC byte_count ;adjust # bytes stored MOV W,eeprom_size ;get memory size MOV W,address-W ;are we past end? SNZ ;if not, skip ahead CLR address ;if so, reset it :done RETP ;leave and fix page bits ; Erase_Mem CLR address ;restore address pointer MOV num_bytes,#eeprom_size ;wipe whole mem :wipeloop CLR data ;byte to wipe with=0 ; MOV data,address ;byte to wipe with=addr CALL I2C_write ;wipe EEPROM byte INC address ;move to next address DJNZ num_bytes,:wipeloop ;Erased enough yet? CLR byte_count ;done, reset stored count CLR save_addr ;reset backup address RETP ;leave and fix page bits ; ;************************** End of I2C Subroutines **************************** ; ;***************************** MAIN PROGRAM CODE ****************************** ; ; ORG 100h ; ; Program execution begins here on power-up or after a reset ; reset_entry mov ra,#%1011 ;initialize port RA mov !ra,#%0100 ;Set RA in/out directions CLR FSR ;reset all ram starting at 08h :zero_ram SB FSR.4 ;are we on low half of bank? SETB FSR.3 ;If so, don't touch regs 0-7 CLR IND ;clear using indirect addressing IJNZ FSR,:zero_ram ;repeat until done mov !option,#%11011111 ;disable rtcc interrupt ; ; Main Program Loop ; :loop MOV W,#55 ;example byte CALL Store_W ;Store byte in next I2c address ; ; <program code goes here> ; JMP :loop ;back to main loop ; ;*************** END ;End of program code
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