UM0934 datasheet(35/113 Pages) STMICROELECTRONICS

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UM0934

MAC layer

Doc ID 17389 Rev 2

35/113

4.9

Additional features

4.9.1

Delta-phase detection at 2400 bps baud rate

When the ST7570 is running at 2400 bps, the delta-phase detection is affected by

±180°

ambiguity, due to the fact that time-slots start alternatively on positive zero-crossing or

negative zero-crossing.

In order to remove such ambiguity, the transmitter can be forced to start the transmission of

a new frame on a positive zero-crossing only. The detection algorithm in the receiver can be

adapted in the same way.

MIB object 0013h (smart-phase detection) can be used to configure this special feature.

Admitted values and corresponding behavior during transmission and reception are shown

in Table 8:

The typical configuration is TX for a Client and RX for a Server.

If enabled, the phase estimated by the smart-phase detection is written in the MIB object

0014h (Phase). This object is updated only when the sender of the frame was an initiator

(i.e. the source MAC address is in the range FIMA – LIMA of the receiver).

Table 8.

Delta-phase detection

Value Name

Behavior

Transmission

Delta-phase detection (reception)

DISA

BLED

The transmission of a new PHY frame starts on

a positive or negative zero-crossing.

Normal.

1TX

The transmission of a new PHY frame starts on

a positive zero-crossing only.

Normal.

2RX

The transmission of a new PHY frame starts on

a positive or negative zero-crossing.

Delta-phase detection is calculated

taking into account all MAC frame

fields.

3TXRX

The transmission of a new PHY frame starts on

a positive zero-crossing only.

Delta-phase detection is calculated

taking into account all MAC frame

fields.

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