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 ph ysical 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 specify a bit order
RS-232 and L IN buses transmit th e LSB (least significa nt bit) first
NOTE. The oscilloscope displays the decode traces and event ta bles for all buses with the M SB on the left and LSB on the right.
For example, an RS-232 signal (after the start b it) might be high, high, high, low, high, low, low, and high. Since the RS-232 protocol
uses high for zero and low for on e, this value would be 0001 0110.
Since the decode displays the MSB first, the oscilloscope reve rses the order of the bits and displays 011 0 1000. If the bus display is
set to hex, th e value displays as 68. If the bus display is set to ASCII, the value displays as h.
RS-232
If you defined an end-of-packet character to
use fo r RS-232 decoding, th e stre am of bytes
will be displayed as packets.
122 MSO4000 and DPO4000 Series Oscilloscopes User Manual
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