PCD5003USLASH10 datasheet(10/44 Pages) PHILIPS

10 / 44 page

1997 Jun 24

Philips Semiconductors

Product speciﬁcation

Advanced POCSAG Paging Decoder

PCD5003

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 codeword in every

18 codewords looking for preamble or sync word. By using

a buffer containing 32 bits (n bits from the current scan,

− 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 codeword (including Idle

codeword) requiring no more than single bit error

correction

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

expected batch position

• When a forced call termination command is received

from an external controller.

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.

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

Call data output format

POCSAG call information is stored in the decoder SRAM

in blocks of 3 bytes per codeword. 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 codeword.

A Message Data block contains the data bits from a

message codeword 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 codeword.

7.15

Sync word indication

The sync word recognized by the PCD5003 is shown in the

call header (bits S3 to S1). The decimal value represents

the identifier number in the EEPROM of the UPSW in

question. A value of 7 indicates the standard POCSAG

sync word.

7.16

Error type indication

Table 10 shows how the different types of detected errors

are encoded in the call data output format.

A message codeword containing more than a single bit

error (bit E3 = 1) may appear as an address codeword

(bit M1 = 0) after error correction. In this event the

codeword is processed as message data and does not

cause call termination.

7.17

Data transfer

Data transfer is initiated either during sync word periods or

as soon as the receiver is disabled after call termination.

If the SRAM buffer is full, data transfer is initiated

immediately during the next codeword.

When the PCD5003 is ready to transfer received call data

an external interrupt will be generated via output INT.

Any message data can be read by accessing the RAM

output register via the I2C-bus interface. Bytes will be

output starting from the position indicated by the RAM read

pointer.

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