
HT9580
32
April 28, 2000
Preliminary
The POCSAG paging code
A transmission using the CCIR Radio paging
Code No.1 (POCSAG code) is generated in ac-
cordance with the following rules (see the fol-
lowing Figure).
-
- )
-
I I I I I I I I I
" 0 0$
! ! "
! ! # $ "
$ #
).
) 8 )
) )
* )
*
% &
"
* 5 0$
' ( )
"
$
)/ $
' ( )
*
*
) 3 $
$
$
*
*
*
*
POCSAG code structure
The transmission is started by sending a pre-
amble, consisting of at least 576 continuously
alternating bits (10101010...). The preamble is
followed by an arbitrary number of batch
blocks.Onlycompletebatchesaretransmitted.
Each batch comprises 17 code-words of 32 bits
each. The first code-word is a synchronization
code-word with fixed pattern. The sync word is
followed by 8 frames (0~7) of 2 code-words each,
containing message information. A code-word
in a frame can either be an address, message or
idle code-word.
Idle code-words also have fixed patterns and
are used to fill empty frames or separate mes-
sages.
Address code-words are identified by an MSB of
logic 0 and are coded as shown in the POCSAG
code structure figure. A user address or RIC
(Receiver Identity Code) consists of 21 bits.
Only the upper 18 bits are encoded in the ad-
dress code-word (bits 2 to 19). The lower 3 bits
designate the frame number in which the ad-
dress is transmitted.
Four different call types can be distinguished
on each user address. The call type is deter-
mined by two functional bits in the address
code-word (bits 20 and 21). The POCSAG stan-
dard recommends the use (in Taiwan) of combi-
nations of data formats and function bits, as
shown in the following table. Other combina-
tions will be set by SPF16~SPF19.
Bit 20 (MSB)
Bit 21 (LSB)
Call Type
Data Format
0
0
Numeric
4-bit package
0
1
Alert only
1
0
Alert only
1
1
Alpha-numeric
7-bit package
Data formats and function bits