CS280

1
EEPROM Memory

• Storing, Reading, and Writing

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

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 not affected if Program Memory is
  rewritten (new program loaded)
• EEPROM can be written/erased at least 100,000
  times

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

Byte 0
0x0000 0x0001 0x0002 0x0003 0x0004 . .
. 0x03FE 0x03FF
Byte 1
Byte 2
Byte 3
Byte 4
Byte 1022
Byte 1023
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

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

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

8
Downloading EEPROM data using Atmon

• Recall You use the WR V command to load the .HEX
  file containing the program and Flash memory data
  to Flash
• Use the WRE V command to load the .EEP file
  containing the EEPROM data

9
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

10
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
• LDI ZL, LOW(values) low 8 bits of the
  address
• LDI ZH, HIGH(values) high 2 bits
• OUT EEARL, ZL write to EEPROM addr reg
• OUT EEARH, ZH
• SBI EECR, 0 set EERE1 (read enable)
• IN temp, EEDR move data to temp register

11
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
• LDI ZL, LOW(values) low 8 bits of the
  address
• LDI ZH, HIGH(values) high 2 bits
• OUT EEARL, ZL write to EEPROM addr reg
• OUT EEARH, ZH
• LDI temp, 0x0A
• OUT EEDR, temp value to be written
• SBI EECR, 2 master write enable
• note EEMWE is cleared automatically after 4
  clock cycles
• SBI EECR, 1 clrd 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