UM0934 datasheet(14/113 Pages) STMICROELECTRONICS

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Physical layer

UM0934

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Doc ID 17389 Rev 2

Physical layer

3.1

Overview

The ST7570 embeds a PHY layer compliant with [2], with additional functions for alarm

management and electrical delta-phase detection.

In order to meet the application’s functions and physical channel characteristics, many

parameters involved at this layer can be programmed by the user.

3.2

Frame structure

The frame at the physical level (PHY_Frame) is made up of 45 bytes (360 bits), as follows:

●

2 bytes - preamble (PRE) (AAAAh)

●

2 bytes - start subframe delimiter (SSD) (54C7h)

●

38 bytes - physical service data unit (P_sdu), i.e. the payload transmitted by the MAC

layer

●

3 bytes - pause or alarm

The bytes are sent from the most significant byte (MSB) to the least significant byte (LSB).

Bits within the byte are packed with the same order.

Figure 2.

Physical frame format

3.3

Frame timing and time-slot synchronization

The time domain in the network is divided into recurrent “time-slots”, with a fixed length

equal to the length of a physical frame PHY_Frame, (45 bytes). The start of each time-slot is

usually aligned with the mains zero-crossing and the bit time is automatically adapted to the

mains frequency and can be chosen from two values:

●

24 bits/mains period

●

48 bits/mains period.

Preamble

(PRE)

Start Subframe

Delimiter

(SSD)

P_sdu

Pause / Alarm

2 bytes

38 bytes

3 bytes

PHY_Frame

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