ST7LITE0 datasheet(16/122 Pages) STMICROELECTRONICS

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ST7LITE0, ST7SUPERLITE

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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 7 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. In a read cycle, the byte to be accessed is

put on the data bus in less than 1 CPU clock cycle.

This means that reading data from EEPROM

takes the same time as reading data from

EPROM, but this memory cannot be used to exe-

cute machine code.

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 PGM bit is set by the software, all the previ-

ous bytes written in the data latches (up to 32) are

programmed in the EEPROM cells. The effective

high address (row) is determined by the last EEP-

ROM write sequence. To avoid wrong program-

ming, the user must take care that all the bytes

written between two programming sequences

have the same high address: only the five Least

Significant Bits of the address can change.

At the end of the programming cycle, the PGM and

LAT bits are cleared simultaneously.

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 ilustrated by the Figure 9.

Figure 7. 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)

E2LAT

CLEARED BY HARDWARE

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