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;**** A P P L I C A T I O N N O T E A V R 1 0 0 ************************ ;* ;* Title: Accessing the EEPROM ;* Version: 2.0 ;* Last updated: 98.06.15 ;* Target: AT90Sxxxx (All AVR Devices) ;* ;* Support E-mail: avr@atmel.com ;* ;* DESCRIPTION ;* This Application note shows how to read data from and write data to the ;* EEPROM. Both random access and sequential access routines are listed. ;* The code is written for 8515, to modify for 4414,2313,2323... apply the ;* following changes: ;* - Remove all entries to EEARH ;* - Rename EEARL to EEAR ;* ;* To modify for 1200, apply the changes above, and change the code ;* as commented inside the routines ;* ;* ;*************************************************************************** .include "8515def.inc" rjmp RESET ;Reset Handle ;*************************************************************************** ;* ;* EEWrite ;* ;* This subroutine waits until the EEPROM is ready to be programmed, then ;* programs the EEPROM with register variable "EEdwr" at address "EEawr:EEawr" ;* ;* Number of words :1200; 5 + return ;* :8515; 7 + return ;* Number of cycles :1200; 8 + return (if EEPROM is ready) ;* :8515; 11 + return (if EEPROM is ready) ;* Low Registers used :None ;* High Registers used:;3 (EEdwr,EEawr,EEawrh) ;* ;*************************************************************************** ;***** Subroutine register variables .def EEdwr =r16 ;data byte to write to EEPROM .def EEawr =r17 ;address low byte to write to .def EEawrh =r18 ;address high byte to write to ;***** Code EEWrite: sbic EECR,EEWE;if EEWE not clear rjmp EEWrite ; wait more ; out EEAR,EEawr;output address for 1200, commented out ! ; the two following lines must be replaced with the line above if 1200 is used out EEARH,EEawrh;output address high for 8515 out EEARL,EEawr;output address low for 8515 out EEDR,EEdwr;output data sbi EECR,EEMWE;set master write enable, remove if 1200 is used sbi EECR,EEWE;set EEPROM Write strobe ;This instruction takes 4 clock cycles since ;it halts the CPU for two clock cycles ret ;*************************************************************************** ;* ;* EERead ;* ;* This subroutine waits until the EEPROM is ready to be programmed, then ;* reads the register variable "EEdrd" from address "EEardh:EEard" ;* ;* Number of words :1200; 5 + return ;* :8515; 6 + return ;* Number of cycles :1200; 8 + return (if EEPROM is ready) ;* :8515; 9 + return (if EEPROM is ready) ;* Low Registers used :1 (EEdrd) ;* High Registers used: :2 (EEard,EEardh) ;* ;*************************************************************************** ;***** Subroutine register variables .def EEdrd =r0 ;result data byte .def EEard =r17 ;address low to read from .def EEardh =r18 ;address high to read from ;***** Code EERead: sbic EECR,EEWE;if EEWE not clear rjmp EERead ; wait more ; out EEAR,EEard;output address for 1200, commented out ! ; the two following lines must be replaced with the line above if 1200 is used out EEARH,EEardh;output address high for 8515 out EEARL,EEard;output address low for 8515 sbi EECR,EERE;set EEPROM Read strobe ;This instruction takes 4 clock cycles since ;it halts the CPU for two clock cycles in EEdrd,EEDR;get data ret ;*************************************************************************** ;* ;* EEWrite_seq ;* ;* This subroutine increments the EEPROM address by one and waits until the ;* EEPROM is ready for programming. It then programs the EEPROM with ;* register variable "EEdwr_s". ;* Number of words :1200; 7 + return ;* :8515; 10 + return ;* Number of cycles :1200; 10 + return (if EEPROM is ready) ;* :8515; 15 + return (if EEPROM is ready) ;* Low Registers used :None ;* High Registers used: :3 (EEdwr_s,EEwtmp,EEwtmph) ;* ;*************************************************************************** ;***** Subroutine register variables .def EEwtmp =r24 ;temporary storage of address low byte .def EEwtmph =r25 ;temporary storage of address high byte .def EEdwr_s =r18 ;data to write ;***** Code EEWrite_seq: sbic EECR,EEWE;if EEWE not clear rjmp EEWrite_seq; wait more ; Write sequence for 1200 ; in EEwtmp,EEAR;get address for 1200, commented out ! ; inc EEwtmp ;increment address 1200, commented out ! ; out EEAR,EEwtmp;output address 1200 ; Write sequence for 8515, must be replaced with the lines above if 1200 is used in EEwtmp,EEARL;get address low 8515 in EEwtmph,EEARH;get address high 8515 adiw EEwtmp,0x01;increment address 8515 out EEARL,EEwtmp;output address 8515 out EEARH,EEwtmph;output address 8515 out EEDR,EEdwr_s;output data sbi EECR,EEMWE;set master write enable, remove if 1200 is used sbi EECR,EEWE;set EEPROM Write strobe ;This instruction takes 4 clock cycles since ;it halts the CPU for two clock cycles ret ;*************************************************************************** ;* ;* EERead_seq ;* ;* This subroutine increments the address stored in EEAR and reads the ;* EEPROM into the register variable "EEdrd_s". ;* Number of words :1200; 5 + return ;* :8515; 7 + return ;* Number of cycles :1200; 8 + return (if EEPROM is ready) ;* :8515; 11 + return (if EEPROM is ready) ;* Low Registers used :1 (EEdrd_s) ;* High Registers used: :2 (EErtmp,EErtmph) ;* ;*************************************************************************** ;***** Subroutine register variables .def EErtmp =r24 ;temporary storage of low address .def EErtmph =r25 ;temporary storage of high address .def EEdrd_s =r0 ;result data byte ;***** Code EERead_seq: sbic EECR,EEWE;if EEWE not clear rjmp EERead_seq; wait more ; The above sequence for EEWE = 0 can be skipped if no write is initiated. ; Read sequence for 1200 ; in EErtmp,EEAR;get address for 1200, commented out ! ; inc EErtmp ;increment address 1200, commented out ! ; out EEAR,EErtmp;output address 1200 ; Read sequence for 8515, must be replaced with the lines above if 1200 is used in EErtmp,EEARL;get address low 8515 in EErtmph,EEARH;get address high 8515 adiw EErtmp,0x01;increment address 8515 out EEARL,EErtmp;output address 8515 out EEARH,EErtmph;output address 8515 sbi EECR,EERE;set EEPROM Read strobe ;This instruction takes 4 clock cycles since ;it halts the CPU for two clock cycles in EEdrd_s,EEDR;get data ret ;**************************************************************************** ;* ;* Test/Example Program ;* ;**************************************************************************** ;***** Main Program Register variables .def counter =r19 .def temp =r20 ;***** Code RESET: ;***** Initialize stack pointer ;* Initialize stack pointer to highest address in internal SRAM ;* Comment out for devices without SRAM ldi r16,high(RAMEND);High byte only required if out SPH,r16 ;RAM is bigger than 256 Bytes ldi r16,low(RAMEND) out SPL,r16 ;***** Program a random location ldi EEdwr,$aa ldi EEawrh,$00 ldi EEawr,$10 rcall EEWrite ;store $aa in EEPROM location $0010 ;***** Read from a random locations ldi EEardh,$00 ldi EEard,$10 rcall EERead ;read address $10 out PORTB,EEdrd;output value to Port B ;***** Fill the EEPROM address 1..64 with bit pattern $55,$aa,$55,$aa,... ldi counter,63;init loop counter clr temp out EEARH,temp;EEARH <- $00 clr temp out EEARL,temp;EEAR <- $00 (start address - 1) loop1: ldi EEdwr_s,$55 rcall EEWrite_seq;program EEPROM with $55 ldi EEdwr_s,$aa rcall EEWrite_seq;program EEPROM with $aa dec counter ;decrement counter brne loop1 ;and loop more if not done ;***** Copy 10 first bytes of EEPROM to r1-r11 clr temp out EEARH,temp;EEARH <- $00 ldi temp,$00 out EEARL,temp;EEAR <- $00 (start address - 1) clr ZH ldi ZL,1 ;Z-pointer points to r1 loop2: rcall EERead_seq;get EEPROM data st Z,EEdrd_s;store to SRAM inc ZL cpi ZL,12 ;reached the end? brne loop2 ;if not, loop more forever:rjmp forever ;eternal loop |