UM0239 datasheet(33/44 Pages) STMICROELECTRONICS

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UM0239

Ping sessions

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When the user clicks PING START, the session begins and the Master sends a series of

packets to one or more Slave devices. All the packets contain the following information:

●

Preamble (0xAAAAAAAA): 4 bytes

●

Header (0x9B58 for Master packets and 0xE958 for Slave packets): 2 bytes

To improve reliability of communications, a FEC algorithm and one redundant byte is used

for each of the following bytes of information:

●

Receiver Address: 1 byte (+ 1 byte for FEC)

●

Transmitter Address: 1 byte (+ 1 byte for FEC)

●

Current Message number: 3 bytes (+ 3 bytes for FEC)

●

Repetition (0x00,0x01,0x02 if the same message has been transmitted once, two or

three times): 1 byte (+ 1 byte for FEC)

●

FCS field, obtained through a calculation of 12 previous bytes: 2 bytes (+ 2 byte for

FEC)

The Slave detects, through the Receiver Address field, if the packet is headed for it or not. If

the message is directed to it, a FCS operation is performed on 12 bytes following the

preamble and the header. The result of calculation is compared with FCS field transmitted

from Master. If the two values differ, an attempt of correction is executed (through FEC

correction code) and a new comparison is performed. If the two FCS fields match, the

message is considered OK from Slave and it is resent to the Master (inverting Master

Address with Slave Address and recalculating FEC and FCS bytes). Otherwise, the

message is considered KO and no response is performed.

An exception occurs when Master transmits the message zero (with Message Number field

0x000000). This message is used to reset the Slave, statistical data collected and no

response to Master is needed.

After a packet transmission, the Master waits (for a time defined in Wait Time in Master

Window) the response from Slave, and if a message headed for it is detected it performs the

same "correctness detection" operation above described in order to consider the message

OK or KO.

Repetition function

To improve the reliability of communications, it is possible to use the repetition function. In

this case, if a response is not detected by Master the packet is sent again for a maximum of

three times before it is definitively considered Not Acknowledged.

Medium access control

A Medium Access Control is also implemented (for both Master and Slave) in order to

prevent two or more devices from transmitting at the same time as described in Table 24 for

the Ping Master parameters and Table 25 for Ping Slave parameters.

Note:

For a low-level description of Ping protocol, please refer to “Power Line Modem Evaluation

FW”.

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