T H E M O D E R M - B U S T E C H N O L O Y
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9.2
Timeouts
Timeouts are a very important part of a communication system. They are used to indicate
meters
that don’t respond. In the case of many clients in the system a situation could occur
when they request all at once. If that is the case these questions will end up in a line that
creates extra waiting time that needs to be considered when setting timeouts.
In the PiiGAB M-Bus 900S/T there are three main timeouts Master timeout, Slave timeout and
Defrag timeout.
9.2.1
Master Timeout
The Master Timeout is the time it takes for an M-Bus telegram to be received by the masterport.
Default is set to 2000ms. The Timeout should be set depending on the baud rate and size of the
telegram.
An M-Bus telegram can be maximum 261 byte long.
Table 9-1
Baudrate
bits/second
Telegram size
(Number of byte x 11 bits)/ba extra time
Timeout
Time in s/ms
300 baud
261 byte (261x11/300)+0,5s
10s / 10000ms
2400 baud
261 byte (261x11/2400)+0,5s
1,7s / 1700ms
9600 baud
261 byte (261x11/9600)+0,5s
0,8s / 800ms
Data collected from the Masterport is send directly to the requested client from the slave port.
9.2.2
Slave Timeout
Slave Timeout is the maximum time it takes to get an answer from the Masterport. The time
varies depending on the amount of clients connected to the PIIGAB M-BUS 900S/T and the
number of telegrams. If the meter responds directly the data is sent directly to the requested
client.
Slave Timeout cannot be shorter than Master Timeout and will be adjusted to Master T
100ms if it is not set to a longer timeout.
In table 9-2 the scenario if the clients ask an M-Bus question at the same time and only read a
maximum telegram of 261 byte is showcased.