Acquire the Signal
Physical Layer Bus Activity
Oscilloscope waveform traces from channels 1 to 4 and the traces you see w hen you choose to display a bus as Bus and
Waveforms always sh ow the physical layer bus activity. In the physical layer display, bits that were transmitted earlier are to
the left, and bits that were transmitted later are to the right.
I2C and CAN buses transmit the MSB (most significant bit) first
SPI buses do not spe cify a bit order
RS-232 and LIN buses transmit the LSB (least significant bit) first
NOTE. The o scilloscope displays the decode traces and event tables for all buses with the MSB on the left and LSB on the right.
For example, an RS-232 sign al (after the start bit) might be high, high, high, low, high, low, low, and high. Since the RS-232 protocol
uses high for zero an d low for one, this value would be 0001 0110.
Since the decode displays the MSB first, the oscilloscope reverses the order of the bits an d displays 0110 1 000. If the bus display is
set to hex, the value displays as 68. If the bus display is set to ASCII, the value displays as h.
DPO3000 Series Oscilloscopes User Manua l 105
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