ATA8742-PXQW【PDF 33/238 页】MCU W/TRANSMITTER ASK/FSK 24QFN

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9151AINDCO07/09

ATA8742

13.3 EEPROM Data Memory

The ATtiny24/44/84 contains 128/256/512 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 Serial data

downloading to the EEPROM, see Serial Downloading on page 184.

13.3.1

EEPROM Read/Write Access

The EEPROM Access Registers are accessible in the I/O space.

The write access times for the EEPROM are given in Table 13-1 on page 39. A self-timing func-

tion, however, lets the user software detect when the next byte can be written. If the user code

contains instructions that write the EEPROM, some precautions must be taken. In heavily fil-

tered power supplies, V

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. See Preventing EEPROM Corruption on page 36 for details on how to avoid

problems in these situations.

In order to prevent unintentional EEPROM writes, a specific write procedure must be followed.

See Atomic Byte Programming on page 33 and Split Byte Programming on page 33 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.

13.3.2

Atomic Byte Programming

Using Atomic Byte Programming is the simplest mode. When writing a byte to the EEPROM, the

user must write the address into the EEARL Register and data into EEDR Register. If the

EEPMn bits are zero, writing EEPE (within four cycles after EEMPE is written) will trigger the

erase/write operation. Both the erase and write cycle are done in one operation and the total

programming time is given in Table 1. The EEPE bit remains set until the erase and write opera-

tions are completed. While the device is busy with programming, it is not possible to do any

other EEPROM operations.

13.3.3

Split Byte Programming

It is possible to split the erase and write cycle in two different operations. This may be useful if

the system requires short access time for some limited period of time (typically if the power sup-

ply voltage falls). In order to take advantage of this method, it is required that the locations to be

written have been erased before the write operation. But since the erase and write operations

are split, it is possible to do the erase operations when the system allows doing time-critical

operations (typically after Power-up).

13.3.4

Erase

To erase a byte, the address must be written to EEAR. If the EEPMn bits are 0b01, writing the

EEPE (within four cycles after EEMPE is written) will trigger the erase operation only (program-

ming time is given in Table 1). The EEPE bit remains set until the erase operation completes.

While the device is busy programming, it is not possible to do any other EEPROM operations.

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