PCD5002 데이터 시트보기 (PDF) - Philips Electronics
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PCD5002 Datasheet PDF : 48 Pages
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Philips Semiconductors
Advanced POCSAG and APOC-1 Paging
Decoder
Product specification
PCD5002
When a message extends beyond the end of a batch no
testing for sync takes place. Instead, a message data
transfer will be initiated by an interrupt to the external
controller. Data reception continues normally after a period
corresponding to the sync word duration.
If any message codeword is found to be uncorrectable, the
‘data fail’ mode is entered and no data transfer will be
attempted at the next sync word position. Instead, a test for
sync word will be carried out.
In the data fail mode message reception continues
normally for 1 batch duration. When a sync word is
detected at the expected position the decoder returns to
the ‘data receive’ mode. If the sync word again fails to
appear, then batch synchronization is deemed lost. Call
reception is then terminated and the ‘fade recovery’ mode
is entered.
The fade recovery mode is intended to scan for sync word
and preamble over an extended window (nominal
position ± 8 bits). This is performed for a period of up to
15 batches, allowing recovery of synchronization from
long fades in the radio signal. Detection of preamble
causes switching to the ‘preamble receive’ mode, while
sync word detection causes switching to the ‘data receive’
mode. When neither is found within a period of 15 batches,
the radio signal is considered lost and the ‘carrier off’ mode
is entered.
The purpose of the 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, 32 −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 causes the
device to switch to the ‘preamble receive’ mode, while
sync word detection causes the device to switch to the
‘data receive’ mode.
handbook, full pagewidth
1997 Jun 24
OFF to ON status
no preamble or
sync word
(3 batches)
switch-on
sync word
preamble
no preamble or
sync word
(1 batch)
preamble receive
sync word
data receive
sync word
no sync word
sync word
sync word
data fail
preamble
no preamble or
sync word
(1 batch)
fade recovery
preamble
no preamble or
sync word
(15 batches)
carrier off
preamble
MLC247
Fig.4 ACCESS® synchronization algorithm for POCSAG.
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