PCD3351AP datasheet(12/36 Pages) PHILIPS

12 / 36 page

1999 Oct 28

Philips Semiconductors

Product speciﬁcation

8-bit microcontrollers with DTMF generator

and 128 bytes EEPROM

PCA3351C; 52C; 53C;

PCD3351A; 52A; 53A

EEPROM AND TIMER 2 ORGANIZATION

The PCD335xA and PCA335xC have 128 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 access

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

operations more efficient, several provisions are available

in the PCD335xA and PCA335xC.

First, the EEPROM array is structured into 32 four-byte

pages (see Fig.5) 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.

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