Amplifiers
4-45
■
Relationship of the CAN Bus Baud Rate and the
Sampling Frequency Set for GX-1
To record without dropping CAN bus data frames, you must use the formula below to
determine the GX-1 lowest sampling frequency, and set that value (or as illustrated
below, an approximation of that value). If the GX-1 data transmission (1 frame for 4
samplings) is faster than the time for one transmission by a CAN bus data frame,
frames will not be dropped.
Conditions for Determining the Sampling Frequency
Time per bit = 1 / Baud-rate
Minimum frame time = data-frame-length x time-per-bit
Data frame length for a standard ID = 44 bits (fixed part)
Data frame length for an extended ID = 62 bits (fixed part)
ITM time = time-per-bit x 3 bits
(When the ITM time is shorter than 25 microseconds, make the ITM time 25
microseconds. 25 microseconds is the delay time output from the CAN con-
troller.)
Sampling frequency
≥
– 1 / [(smallest-frame-time + ITM-time) / 4]
Example
When the CAN bus Baud rate is 500 Kbps for a standard ID:
Time per bit = 1 / 500 K = 2 µ sec/bit
Minimum frame time = 44
✕
2 µ sec = 88 µ sec
ITM time = 2 µ sec
✕
3 bit = 6 µ sec
(... 6 µ < 25 µ so set the ITM time to 25 µ sec.)
Sampling frequency
≥
– 1 / [(88 µ sec + 25 µ sec) /4] = 38.835 kHz
(The lowest sampling frequency of the GX-1 becomes the approximation of 50
kHz, a near approximation higher than the above 38.835 kHz.)
CAN bus Baud rate
GX-1 sampling frequency (standard ID)
GX-1 sampling frequency (extended ID)
50 Kbps
5 kHz
5 kHz
100 Kbps
10 kHz
10 kHz
250 Kbps
20 kHz
20 kHz
500 Kbps
50 kHz
50 kHz
1 Mbps
100 kHz
50 kHz
Using the multi-sampling function, the Base Sample setting for other analog channels
can be set to 1/10 of the above sampling frequencies.
Examples of CAN bus Baud rates and sampling frequencies:
Содержание GX-1
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