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Acquire the Signal
Physical Layer Bus Activity
Oscilloscope waveform traces from analog channels 1 to 4, digital channels D15 to D0, and the traces you see when you choose to
display a bus always show 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 signi fi cant bit) fi rst
SPI buses do not specify a bit order
RS-232 and LIN buses transmit the LSB (least signi fi cant bit) fi rst
NOTE. The oscilloscope 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 signal (after the start bit) might be high, high, high, low, high, low, low, and high. Since the RS-232 protocol
uses high for zero and low for one, this value would be 0001 0110.
Since the decode displays the MSB fi rst, the oscilloscope reverses the order of the bits and displays 0110 1000. 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.
RS-232
If you de fi ned an end-of-packet character to
use for RS-232 decoding, the stream of bytes
will be displayed as packets.
122 MSO4000 and DPO4000 Series Oscilloscopes User Manual