PCD5003USLASH10 datasheet(9/44 Pages) PHILIPS

9 / 44 page

1997 Jun 24

Philips Semiconductors

Product speciﬁcation

Advanced POCSAG Paging Decoder

PCD5003

To allow easy oscillator adjustment (e.g. by means of a

variable capacitor) a 32.768 kHz reference frequency can

be selected at output REF by SPF programming.

7.10

Input data processing

Data input is binary and fully asynchronous. Input bit rates

of 512, 1200 and 2400 bits/s are supported. As a

programmable option, the polarity of the received data can

be inverted before further processing.

The input data is noise filtered by means of a digital filter.

Data is sampled at 16 times the data rate and averaged by

majority decision.

The filtered data is used to synchronize an internal clock

generator by monitoring transitions. The recovered clock

phase can be adjusted in steps of 1

⁄8 or 1⁄32 bit period per

received bit.

The larger step size is used when bit synchronization has

not been achieved, the smaller when a valid data

sequence has been detected (e.g. preamble or sync

word).

7.11

Battery saving

Current consumption is reduced by switching off internal

decoder sections whenever the receiver is not enabled.

To further increase battery efficiency, reception and

decoding of an address codeword is stopped as soon as

the uncorrected address field differs by more than 3 bits

from the enabled RICs. If the next codeword must be

received again, the receiver is re-enabled thus observing

the programmed establishment times tRXE and tRDE.

The current consumption of the complete pager can be

minimized by separately activating the RF oscillator circuit

(at output ROE) before activating the rest of the receiver.

This is possible with the UAA2082 receiver which has

external biasing for the oscillator circuit.

7.12

Synchronization strategy

In ON status the PCD5003 synchronizes to the POCSAG

data stream by means of the Philips ACCESS® algorithm.

A flow diagram is shown in Fig.4. Where ‘sync word’ is

used, this implies both the standard POCSAG sync word

and any enabled User Programmable Sync Word

(UPSW).

Several modes of operation can be distinguished

depending on the synchronization state. Each mode uses

a different method to obtain or retain data synchronization.

The receiver and oscillator enable outputs (respectively

RXE and ROE) are switched accordingly, with the

appropriate establishment times (respectively tRXON and

tROON).

Before comparing received data with preamble, an

enabled sync word or programmed user addresses, the

appropriate error correction is applied.

Initially, after switching to ON status, the decoder is in

switch-on mode. Here the receiver will be enabled for a

period up to 3 batches, testing for preamble and sync

word. Failure to detect preamble or sync word will cause

switching to ‘carrier off’ mode.

Detection of preamble switches to preamble receive

mode, in which sync word is looked for. The receiver will

remain enabled while preamble is detected. When neither

sync word nor preamble is found within 1 batch duration

‘carrier off’ mode is entered.

Upon detection of a sync word the data receive mode is

entered. The receiver is activated only during enabled user

address frames and sync word periods. When an enabled

user address has been detected, the receiver will be kept

enabled for message codeword reception until the call

termination criteria are met.

During call reception data bytes are stored in an internal

SRAM buffer, capable of storing 2 batches of message

data.

Messages are transmitted contiguously, only interrupted

by sync words at the beginning of each batch. When a

message extends beyond the end of a batch, no testing for

sync takes place. Instead, a message data transfer will be

initiated by an interrupt to the external controller. Data

reception continues normally after a period corresponding

to the sync word duration.

If any message codeword is found to be uncorrectable,

‘data-fail’ mode is entered and no data transfer will be

attempted at the next sync word position. Instead, a test for

sync word will be carried out.

In the data fail mode message reception continues

normally for 1 batch duration. Upon detection of sync word

at the expected position the decoder returns to

‘data receive’ mode. If sync word again fails to appear,

batch synchronization is deemed lost. Call reception is

then terminated and ‘fade recovery’ mode is entered.

The fade recovery mode is intended to scan for sync word

and preamble over an extended window (nominal

position

±8 bits).

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