Service manual

June 21, 2004 1-21
NP88 FLEX GENERAL
Paging Coding Schemes
Eleven message blocks containing interleaved data follow the sync block. Data is
interleaved within the message blocks t o provide signal fading protection for up to
10 msec. The message blocks contain frame and system information, addresses,
vector a nd original data.
Eachaddress hasanassociatedvector whichspecifiesthemessage type and points
to the beginning of the message data. The FLEX code provides five billion address
combinations.
When the pager is turned on, it performs a search for a F L EX frame. The duration
of the search is programmable from 1 to 4 minutes. When a valid frame is received,
the pager decodes the frame number to determine where it is in the FLEX cycle.
The pager decodes future frames based on two parameters, home frame and
collapse, which are programmed with its address. The pager a lways decodes its
programmed home frame.
For example, if the pager is programmed for frame 10, and collapse 2, the decode
frequency is equal to 2
2
frames or every four frames. Therefore, the pager decodes
frames 10, 14, 18, 22, 26, and so o n.
Inadditiontotheprogrammedcollapseparameter,asystemcollapseistransmitted
as part of the FLEX frame. The pager uses the smaller of the two collapse values
to determine the frequency of frame decoding.
Iftheinitialsearchtime endsandthepager hasnotfoundaFLEXframe,thepa ger
changes to a baudsearch mode where it “wakes up” every 1.6secondsand looks for
asignalonthechannelforapproximately80milliseconds.Ifthebaudsearchdetects
a signal, the pager then begins another search for a FLEX frame.