RTU message framing

In RTU mode, the message begins with a gap in transmission of at least 3.5 character

periods. Network components monitor the bus continuously and when a ‘silent’ period

of more than 3.5 character periods is detected, the first character following the

transmission gap is translated to determine if it corresponds to the device’s own

address.

The end of the transmitted message is marked by a further interval of at least 3.5

character periods duration. An new message can only begin after this interval.

The entire message field must be transmitted as a continuous stream. If an interval of

more than 1.5 character periods is detected during transmission of the message, then

the message is assumed to be incomplete and the device returns to waiting for the

next device address. The action taken on receipt  of an incomplete message is as for

receipt of an incorrect message, and it is ignored.

If a new message begins within 3.5 characters periods of the end of the previous

frame, the device again ignores the message.