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ST7580

Physical layer

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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

1

1200

FSK @2400

2400

1

2400

FSK @4800

4800

1

4800

FSK @9600

9600

1

9600