PCD5003 datasheet(7/44 Pages) PHILIPS

7 / 44 page

1997 Jun 24

Philips Semiconductors

Product speciﬁcation

Advanced POCSAG Paging Decoder

PCD5003

Alert-only calls only consist of a single address codeword.

Numeric and alphanumeric calls have message

codewords following the address. A message causes the

frame structure to be temporarily suspended. Message

codewords are sent until the message is completed, with

only the sync words being transmitted in their expected

positions.

Message codewords are identified by an MSB of logic 1

and are coded as shown in Fig.3. The message

information is stored in a 20-bit field (bits 2 to 21). The data

format is determined by the call type: 4 bits per digit for

numeric messages and 7 bits per (ASCII) character for

alphanumeric messages.

Each codeword is protected against transmission errors by

10 CRC check bits (bits 22 to 31) and an even-parity bit

(bit 32). This permits correction of maximum 2 random

errors or up to 3 errors in a burst of 4 bits (a 4-bit burst

error) per codeword.

The POCSAG standard recommends the use of

combinations of data formats and function bits, as given in

Table 1. Other (non-standard) combinations will be

received normally by the PCD5003. Message data is not

deformatted.

Table 1

POCSAG recommended call types and function bits

BIT 20 (MSB)

BIT 21 (LSB)

CALL TYPE

DATA FORMAT

numeric

4-bits per digit

alert only 1

−

alert only 2

−

alphanumeric

7-bits per ASCII character

Fig.3 POCSAG code structure.

handbook, full pagewidth

PREAMBLE

BATCH 1

BATCH 2

BATCH 3

LAST BATCH

SYNC | CW CW | CW CW | . . . . . | CW CW

FRAME 0

FRAME 1

FRAME 7

10101 . . . 10101010

Address code-word

Message code-word

18-bit address

2 function bits

10 CRC bits

20-bit message

10 CRC bits

MCD456

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