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Design and Implementation of a Practical FLEX Paging Decoder

Grayson Wireless 8

2.3.1 Frame Format

The format of each frame is shown in Figure 2-4 [Ste 96b]. Each frame contains a

synchronization period (Sync) of 115 ms and then 11 blocks of data with each block having a

duration of 160 ms. Blocks are numbered 0 to 10.

Sync Block 0

Sync 1 Sync 2

115 ms

25 ms90 ms

Block 1 Block 10

160 ms

1875 ms

Frame

Info

Figure 2-4

Frame format

The synchronization period contains two synchronization periods. The first synchronization

period (Sync1 and Frame Info) is always sent at 1600 bps. Due to the proprietary nature of the

FLEX protocol, the exact format of Sync1, Frame Info, and Sync2 cannot be discussed. Only

important facts about each one will be discussed here so that a complete overview of the protocol

can be given. Sync1 contains two 32-bit synchronization words that are separated by 16 dotting

bits. These words are unique and identify the baud rate (1600 or 3200) and the modulation type

(2-FSK or 4-FSK) of Sync2 and the data blocks. The frame information which is between Sync1

and Sync2 identifies the current frame number and cycle number. The total number of bits in

Sync1 and Frame Info are 144 bits @ 1600 bps which is 90 ms in duration. Following Frame

Info is the second synchronization period (Sync 2) which is 25 ms long. This synchronization is

designed to train the receiver and decoder to the new modulation and baud rate.

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Motorola Pro FLX Manuel d'utilisateur Page 16