PCF5001H データシートの表示（PDF） - Philips Electronics

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PCF5001H

POCSAG Paging Decoder

Philips Electronics 

Philips Semiconductors

POCSAG Paging Decoder

Product specification

PCF5001

7.2 The POCSAG paging code

A transmission using the “CCIR Radio paging Code No. 1”

(POCSAG code) is constructed in accordance with the

following rules (see Fig.5).

The transmission is started by sending a preamble,

consisting of at least 576 continuously alternating bits

(10101010...). The preamble is followed by an arbitrary

number of batch blocks. Only complete batches are

transmitted.

Each batch comprises 17 codewords of 32 bits each.

The first codeword is a synchronization codeword with a

fixed pattern. The sync word is followed by 8 frames

(0 to 7) of 2 codewords each, containing message

information. A codeword in a frame can either be an

address, message or idle codeword.

Idle codewords also have a fixed pattern and are used to

fill empty frames or to separate messages.

Address codewords are identified by an MSB at logic 0

and are coded as shown in Fig.5. A user address or RIC

consists of 21 bits. Only the upper 18 bits are encoded in

the address codeword (bits 2 to 19). The lower 3 bits

designate the frame number (0 to 7) in which the address

is transmitted.

Four different call types (‘numeric’, ‘alphanumeric’ and two

‘alert only’ types) can be distinguished. The call type is

determined by two function bits in the address codeword

(bits 20 and 21).

Alert-only calls consist only 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 at logic 1

and are coded as shown in Fig.5. The message

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

The standard 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 a maximum of 2 random

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

error) per codeword.

handbook, full pagewidth

PREAMBLE BATCH 1

BATCH 2

BATCH 3

LAST BATCH

10101 . . . 10101010

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

FRAME 0 FRAME 1

FRAME 7

Address code-word 0 18-bit address 2 function bits 10 CRC bits P

Message code-word 1 20-bit message

10 CRC bits P

MCD456

Fig.5 POCSAG code structure.

1997 Mar 04

10

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