ST72340 datasheet(19/191 Pages) STMICROELECTRONICS

19 / 191 page

ST72340, ST72344, ST72345

19/191

DATA EEPROM (Cont’d)

5.3 MEMORY ACCESS

The Data EEPROM memory read/write access

modes are controlled by the E2LAT bit of the EEP-

ROM Control/Status register (EECSR). The flow-

chart in Figure 8 describes these different memory

access modes.

Read Operation (E2LAT = 0)

The EEPROM can be read as a normal ROM loca-

tion when the E2LAT bit of the EECSR register is

cleared.

On this device, Data EEPROM can also be used to

execute machine code. Take care not to write to

the Data EEPROM while executing from it. This

would result in an unexpected code being execut-

ed.

Write Operation (E2LAT = 1)

To access the write mode, the E2LAT bit has to be

set by software (the E2PGM bit remains cleared).

When a write access to the EEPROM area occurs,

the value is latched inside the 32 data latches ac-

cording to its address.

When E2PGM bit is set by the software, all the

previous bytes written in the data latches (up to

32) are programmed in the EEPROM cells. The ef-

fective high address (row) is determined by the

last EEPROM write sequence. To avoid wrong

programming, the user must take care that all the

bytes written between two programming sequenc-

es have the same high address: only the five Least

Significant Bits of the address can change.

The programming cycle is fully completed when

the E2PGM bit is cleared.

Note: Care should be taken during the program-

ming cycle. Writing to the same memory location

will over-program the memory (logical AND be-

tween the two write access data result) because

the data latches are only cleared at the end of the

programming cycle and by the falling edge of the

E2LAT bit.

It is not possible to read the latched data.

This note is illustrated by the Figure 10.

Figure 8. Data EEPROM Programming Flowchart

READ MODE

E2LAT = 0

E2PGM = 0

WRITE MODE

E2LAT = 1

E2PGM = 0

READ BYTES

IN EEPROM AREA

WRITEUPTO 32 BYTES

IN EEPROM AREA

(with the same 11 MSB of the address)

START PROGRAMMING CYCLE

E2LAT=1

E2PGM=1 (set by software)

E2PGM

CLEARED BY HARDWARE

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