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PCD5003AH

Enhanced Pager Decoder for POCSAG

Philips Electronics 

Philips Semiconductors

Enhanced Pager Decoder for POCSAG

Product specification

PCD5003A

If any message code-word 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).

This is done for a period of up to 15 batches, allowing

recovery of synchronization from long fades in the radio

signal. Detection of preamble switches to

‘preamble receive’ mode, while sync word detection

switches to ‘data receive’ mode. When neither is found

within a period of 15 batches, the radio signal is

considered lost and ‘carrier off’ mode is entered.

The purpose of carrier off mode is to detect a valid radio

transmission and synchronize to it quickly and efficiently.

Because transmissions may start at random, the decoder

enables the receiver for 1 code-word in every

18 code-words looking for preamble or sync word.

By using a buffer containing 32 bits (n bits from the current

scan, 32 − n from the previous scan) effectively every

batch bit position can be tested within a continuous

transmission of at least 18 batches. Detection of preamble

switches to ‘preamble receive’ mode, while sync word

detection switches to ‘data receive’ mode.

7.13 Call termination

Call reception is terminated:

• Upon reception of any address code-word (including idle

code-word) requiring no more than single bit error

correction

• Upon reception of a correctable address code-word

(error type other than ‘111’; see Table 10) that matches

an enabled RIC

• When a forced call termination command is received

from an external controller.

• In ‘data fail’ mode, when a sync word is not found at the

expected batch position.

The last method permits an external controller to stop call

reception depending on the number and type of errors

which occurred in a call. After a forced call termination the

decoder will enter ‘data fail’ mode.

The type of error correction as well as the call termination

conditions are indicated by status bits in the message data

output.

In the event of the terminating code-word matching an

enabled RIC, a concatenated call will be started with the

call header replacing the terminator of the previous call.

Following call termination, transfer of the data received

since the previous sync word period is initiated by means

of an interrupt to the external controller.

7.14 Enhanced call termination

The PCD5003A provides an enhanced mode of call

termination which is enabled by setting SPF byte 3, bit D7.

When enabled, the following call termination conditions

apply, in addition to those listed in Section 7.15.

• Reception of two consecutive code-words (excluding

sync word), each of which are either uncorrectable or an

address code-word with more than one bit in error.

7.15 Call data output format

POCSAG call information is stored in the decoder SRAM

in blocks of 3 bytes per code-word. Each stored call

consists of a call header, followed by message data blocks

and concluded by a call terminator. In the event of

concatenated messages the call terminator is replaced

with the call header of the next message. An alert-only call

only has a call header and a call terminator.

The formats of a call header, a message data block and a

call terminator are shown in Tables 4, 6 and 8.

A Call Header contains information on the last sync word

received, the RIC which began call reception and the type

of error correction performed on the address code-word.

A Message Data block contains the data bits from a

message code-word plus the type of error correction

performed. No deformatting is done on the data bits:

numeric data appear as 4-bit groups per digit,

alphanumeric data have a 7-bit ASCII representation.

The Call Terminator contains information on the last sync

word received, information on the way the call was

terminated (forced call termination command, loss of sync

word in ‘data fail’ mode) and the type of error correction

performed on the terminating code-word.

1999 Jan 08

10

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