AT90PWM2_10 Datasheet, PDF (20/361 Pages) ATMEL Corporation – 8-bit Microcontroller with 8K Bytes In-System Programmable Flash

Figure 3. On-chip Data SRAM Access Cycles
T1
T2
T3
clk
CPU
Address
Data
WR
Data
RD
Compute Address
Address valid
Memory Access Instruction
Next Instruction
6.3 EEPROM Data Memory
The AT90PWM2/2B/3/3B contains 512 bytes of data EEPROM memory. It is organized as a
separate data space, in which single bytes can be read and written. The EEPROM has an
endurance of at least 100,000 write/erase cycles. The access between the EEPROM and the
CPU is described in the following, specifying the EEPROM Address Registers, the EEPROM
Data Register, and the EEPROM Control Register.
For a detailed description of SPI and Parallel data downloading to the EEPROM, see “Serial
Downloading” on page 293, and “Parallel Programming Parameters, Pin Mapping, and Com-
mands” on page 282 respectively.
6.3.1
EEPROM Read/Write Access
The EEPROM Access Registers are accessible in the I/O space.
The write access time for the EEPROM is given in Table 6-2. A self-timing function, however,
lets the user software detect when the next byte can be written. If the user code contains instruc-
tions that write the EEPROM, some precautions must be taken. In heavily filtered power
supplies, V_CC is likely to rise or fall slowly on power-up/down. This causes the device for some
period of time to run at a voltage lower than specified as minimum for the clock frequency used.
For details on how to avoid problems in these situations seeSee “Preventing EEPROM Corrup-
tion” on page 25.
In order to prevent unintentional EEPROM writes, a specific write procedure must be followed.
Refer to the description of the EEPROM Control Register for details on this.
When the EEPROM is read, the CPU is halted for four clock cycles before the next instruction is
executed. When the EEPROM is written, the CPU is halted for two clock cycles before the next
instruction is executed.
6.3.2 The EEPROM Address Registers – EEARH and EEARL
Bit
15
14
13
12
11
10
9
8
–
–
–
–
–
–
–
EEAR8 EEARH
20 AT90PWM2/3/2B/3B
4317J–AVR–08/10