HT9480 datasheet(19/47 Pages) HOLTEK

19 / 47 page

HT9480

Rev. 1.20

July 31, 2002

The two function bits (bits 20 and 21) allow distinction

of four different calls to one user address as shown in

following Table.

Bit 20

(MSB)

Bit 21

(LSB)

Call Type

Data Format

Numeric

4-bits per digit

Alert only

Alpha-numeric

7-bits per ASCII

character

An idle codeword is a valid address codeword, which

cannot be allocated to the pager.

There is a total of 20 bits of caller information to be put

into a message codeword (bits 2 to 21), which is pro-

tected by the CRC checkbits (bits 22 to 31).

· Decoding of the POCSAG data stream

The POCSAG coded input data received from RF

module is first filtered by an internal digital filter in the

decoder. From the filtered data, a sampling clock syn-

chronous to the data rate is derived. The decoder sup-

ports 512, 1200, and 2400 bits per second data rate,

which in turn results in their corresponding sampling

clock frequency.

Upon detection of a valid call, the decoder performs

several operations (refer to the following section of

the Message Data Transfer).

Call termination is normally deemed when a valid idle

or another address codeword is received after a mes-

sage code word.

· Erroneous codewords

Upon receipt of erroneous uncorrectable codewords,

call termination occurs according to the conditions

given below:

SPF08 SPF09

Call Termination Event

Any two consecutiv ecodewords

or the codeword directly following

the address codeword in error

Any single codeword in error

Any two consecutive codewords in

error

Error correction

Item

Description

Preamble

4 random errors in 31 bits

Synchronization

code-word

2 random errors in 32 bits

Address

code-word

2 random errors, or 4-bit burst

errors (optional)

Message

code-word

2 random errors, or 4-bit burst

errors (optional)

In the HT9480 error correction methods have been im-

plemented as shown in above Table.

Random error correction is default for both address and

message code-words. Burst error correction can be

switched by SPF 15. Up to 4 bits of burst errors can be

corrected.

P R E A M B L E

B A T C H 1

B A T C H 2

L A S T B A T C H

1 0 1 0 . . . . . . . . . 1 0 1 0 1 0 1 0 1 0

. R A M E 0

. R A M E 1

. R A M E 7

1 8 A d d r e s s B i t s

A d d r e s s c o d e w o r d

M e s s a g e c o d e w o r d

B i t N u m b e r

2 t o 1 9

2 0 / 2 1

2 2 t o 3 1

3 2

3 1 I d l e c o d e B i t p a t t e r n

I d l e c o d e w o r d

3 1 S y n c h c o d e B i t p a t t e r n

S y n c h c o d e w o r d

1 0 C R C b i t s

2 0 M e s s a g e B i t s

S y n c h

C W

2 . u n c t i o n

B i t s

1 0 C R C b i t s

C W

POCSAG code structure

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