PCD3354AH データシートの表示（PDF） - Philips Electronics

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PCD3354AH

8-bit microcontrollers with DTMF generator and 256 bytes EEPROM

Philips Electronics 

Philips Semiconductors

8-bit microcontrollers with DTMF

generator and 256 bytes EEPROM

Product specification

PCA3354C; PCD3354A

7 EEPROM AND TIMER 2 ORGANIZATION

The PCA3354C; PCD3354A have 256 bytes of Electrically

Erasable Programmable Read Only Memory (EEPROM).

Such non-volatile storage provides data retention without

the need for battery backup. In telecom applications, the

EEPROM is used for storing redial numbers and for short

dialling of frequently used numbers. More generally,

EEPROM may be used for customizing microcontrollers,

such as to include a PIN code or a country code, to define

trimming parameters, to select application features from

the range stored in ROM.

The most significant difference between a RAM and an

EEPROM is that a bit in EEPROM, once written to a

logic 1, cannot be cleared by a subsequent write

operation. Successive write accesses actually perform a

logical OR with the previously stored information.

Therefore, to clear a bit, the whole byte must be erased

and re-written with the particular bit cleared. Thus, an

erase-and-write operation is the EEPROM equivalent of a

RAM write operation.

Whereas read access times to an EEPROM are

comparable to RAM access times, write and erase

accesses are much slower at 5 ms each. To make these

operations more efficient, several provisions are available

in the PCA3354C; PCD3354A.

First, the EEPROM array is structured into 64 four-byte

pages (see Fig.4) permitting access to 4 bytes in parallel

(write page, erase/write page and erase page). It is also

possible to erase and write individual bytes.

Finally, the EEPROM address register provides

auto-incrementing, allowing very efficient read and write

accesses to sequential bytes.

To simplify the erase and write timing, the derivative 8-bit

down-counter (Timer 2) with reload register is provided.

In addition to EEPROM timing, Timer 2 can be used for

general real-time tasks, such as for measuring signal

duration and for defining pulse widths.

1996 Dec 18

11

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