ST7580 datasheet(25/33 Pages) STMICROELECTRONICS

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ST7580

Physical layer

9.1.2

PSK physical frame

Figure 11

shows the physical frame for PSK modulations.

Figure 11. PSK physical frame structure (length in bytes)

The meaning of each field is as follows:



Preamble: a sequence of alternating 1 and 0 symbols (AAh bytes) required by the

receiver PLL to achieve bit synchronization. Its length is programmable from 2 to 5

bytes.



Unique word: a predefined sequence used to mark the start of a physical frame. The

physical layer also provides SNR estimation on the received unique word.



Mode: indicates the PSK mode used for the physical SDU. Thanks to this byte, the

receiver can automatically detect the PSK mode to be used to properly receive the

physical SDU.



Physical SDU (service data unit): payload of the physical layer. Its length is specified in

its first byte, which is always present.

Preamble, unique word, and mode fields are always transmitted using the B-PSK

modulation. The physical layer SDU field can be sent according to any PSK modulation

(B-PSK, Q-PSK, 8-PSK, B-PSK coded, Q-PSK coded, B-PSK coded PNA) expressed in the

mode field.

9.2

FSK modulations

9.2.1

FSK options

The ST7580 supports several FSK (frequency shift keying) modulations with a symbol rate

from 1200 to 9600 baud. Table 11 summarizes all the available FSK modulations and their

bit rate.

The frequency deviation (

f) is the difference between the carrier frequency and the FSK

tone.

Table 11. FSK modes description

Modulation

Symbol rate [baud]

Information bits per symbol

Bit rate [bps]

FSK @1200

1200

FSK @2400

2400

FSK @4800

4800

FSK @9600

9600

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