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EEPROM Memory

EEPROM Memory. Storing, Reading, and Writing. Atmega32 Memory. Address bus (16-bit in Atmega32) A unique 16-bit address references each memory byte. Data bus (8-bit). Nonvolatile – ROM (fast R – slow W) ROM PROM EPROM EEPROM (permanent data store) Flash ROM (program store).

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EEPROM Memory

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  1. EEPROM Memory Storing, Reading, and Writing CS-280 Dr. Mark L. Hornick

  2. Atmega32 Memory • Address bus (16-bit in Atmega32) • A unique 16-bit address references each memory byte. • Data bus (8-bit) • Nonvolatile – ROM (fast R – slow W) • ROM • PROM • EPROM • EEPROM (permanent data store) • Flash ROM (program store) • Volatile – RAM (fast RW) • SRAM (temp data store) • DRAM CS-280 Dr. Mark L. Hornick

  3. EEPROM is non-volatile memory • Power does not have to be supplied to maintain values stored in EEPROM • EEPROM values are maintained when power is shut off • EEPROM is (generally) not affected if Program Memory is rewritten (new program loaded) • EEPROM can be written/erased at least 100,000 times CS-280 Dr. Mark L. Hornick

  4. EEPROM Memory Addressing • EEPROM is organized and accessed in bytes, as in SRAM • There are 1024 bytes of EEPROM • Each byte has a unique 16-bit address • But since there are only 1024 bytes of EEPROM, only 10 bits are used • The first byte of EEPROM is at address 0x0000 • As compared to SRAM, which starts at 0x0060 0x0000 0x0001 0x0002 0x0003 0x0004 . . . 0x03FE 0x03FF Byte 0 Byte 1 Byte 2 Byte 3 Byte 4 Byte 1022 Byte 1023 CS-280 Dr. Mark L. Hornick

  5. Data can be stored in EEPROM via the .db directive .ESEG ; switch further directives to EEPROM segment .ORG 0x0000 ; set addr for start of EEPROM x1: .db 1,5 ; alloc 2 bytes in EEPROM with initial values of 1 and 5 title: .db ‘c’,’e’,’2’,’8’,’0’, ‘0’,0 ; allocate 7 bytes in EEPROM course: .db “CE-2800”, 0 ; allocate 8 bytes in EEPROM Note assembler does NOT automatically insert a NULL char at the end of the string • The .db n,m,… (“define byte”) directive tells the assembler to allocate and store the bytes n,m… in EEPROM • The initial values of the memory are specified, as with Program Memory CS-280 Dr. Mark L. Hornick

  6. The AVR Assembler creates a separate file (with the .EEP extension) containing EEPROM data • You have to load the EEPROM values as a separate step in AVR Studio • Recall: The .HEX file contains opcodes for the program as well as Flash memory data CS-280 Dr. Mark L. Hornick

  7. Downloading EEPROM data in AVR Studio • From the Debug menu, select the “Up/Download Memory” command • The debugger must be running for this command to become enabled • The EEPROM data is in an “.eep” file, NOT the “.hex” file CS-280 Dr. Mark L. Hornick

  8. Reading data from EEPROM There are no specific instructions to load (read) data from EEPROM Instead, EEPROM is accessed as if it were an I/O Subsystem • EEPROM is accessed via Special-purpose I/O Registers • EECR – Control Register • EEARH – Address Register (high 2 bits) • EEARL – Address Register (low 8 bits) • EEDR - Data Register CS-280 Dr. Mark L. Hornick

  9. Using EEPROM I/O Registersto read EEPROM data .ESEG ; put data in EEPROM values: .db 1,2,3,4,5 .CSEG CLR temp OUT EECR, temp ; clear EECR bits ; load the address of EEPROM data we want to read LDI ZL, LOW(values) ; low 8 bits of the address LDI ZH, HIGH(values) ; high 2 bits OUT EEARL, ZL ; set EEPROM address OUT EEARH, ZH ;next, tell the EEPROM we want to read it SBI EECR, 0 ; set EERE=1 (read enable) ; after SBI, the EEPROM value is in the EEDR register ; finally, move the value in EEDR to a regular register IN temp, EEDR ; move data to temp register CS-280 Dr. Mark L. Hornick

  10. Using EEPROM I/O Registersto write EEPROM data .ESEG ; reserve space in EEPROM values: .byte 5 .CSEG CLR temp OUT EECR, temp ; clear EECR bits ; load the address of EEPROM data we want to write LDI ZL, LOW(values) ; low 8 bits of the address LDI ZH, HIGH(values) ; high 2 bits OUT EEARL, ZL ; set EEPROM address OUT EEARH, ZH Wait: SBIC EECR, 1 ; check if EEWE is clear (write not in progress) RJMP wait ; loop back if not clear (takes several ms) LDI temp, ‘a’ ; the value to be written to EEPROM OUT EEDR, temp ; move the value to EEDR SBI EECR, 2 ; bit EEMWE: master write enable ; note: EEMWE is cleared automatically after 4 clock cycles SBI EECR, 1 ; bit EEWE: clr’d automatically after write EEWE is cleared automatically after the byte is actually written, but each EEPROM write takes several ms, so EEWE will remain set for some time CS-280 Dr. Mark L. Hornick

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