82 EM-ABS-01 for ACU 03/12
7.14.3 Capacity planning of the system bus
Each PDO telegram possesses a constant useful data content of 8 Bytes. According to
worst case, this results in a maximum telegram length of 140 bits. The maximum
telegram run time of the PDOs is thus stipulated via the set baud rate.
Capacity planning
Baud rate
kBaud
Telegram runtime
μs
1000 140
500 280
250 560
125 1120
100 1400
50 2800
As a function of the set baud rate and the transmission interval of the TxPDOs se-
lected, the following bus loads results:
Capacity of the system bus
Baud
rate /
kBaud
Bus load as a function of the transmission for one TxPDO in %
1ms 2ms 3ms 4ms 5ms 6ms 7ms 8ms 9ms 10ms
1.000 14 7 4,7 3,5 2,8 2,3 2 1,8 1,6 1,4
500 28 14 9,3 7 5,6 4,7 4 3,5 3,1 2,8
250 56 28 18,7 14 11,2 9,3 8 7 6,2 5,6
125 112 56 37,3 28 22,4 18,7 16 14 12,4 11,2
100 140 70 46,7 35 28 23,3 20 17,5 15,6 14
50 280 140 93,3 70 56 46,7 40 35 31,1 28
Atten-
tion:
A bus load >100% means that a telegram cannot be dispatched com-
pletely between two transmission times.
Such a setting is not admissible!
This observation must be done for each TxPDO. The sum of all the TxPDOs decides
on the entire bus load. The bus load must be designed in such a way that any tele-
gram repetitions for transmission errors are possible without exceeding the bus ca-
pacity.
Note: To facilitate capacity planning, a Microsoft Excel file with the name
"Load_Systembus.xls” is available.
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