Rigol MSO4000 User Manual page 174

RIGOL
In RS232, you need to set the start bit, data bits, check bit (optional) and stop bit of
each frame of data.
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Data Bits
Start Bit: represents when the data begins. Setting the Polarity is equivalent to
specifying the "Start Bit".
Data Bits: represents the number of data bits actually contained in each frame of
data.
Even-OddCheck: check the correctness of the data transmission.
Odd-Check: the number of "1" in the data bit and check bit is an odd. For
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example, when 0x55 (01010101) is sent, a 1 needs to be filled in the check bit to
make the number of 1 to be an odd.
Even Check: the number of "1" in data bit and check bit is an even. For example,
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when 0x55 (01010101) is sent, a 0 should be filled in the check bit.
None: no check bit during the transmission.
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Press Decode1  Decode to select "RS232" to open the RS232 decoding function
menu.
1. TX and RX Channel Setting
Press TX to select any channel (CH1 to CH4 or D0-D15) as the transmitting
channel and when "OFF" is selected, no transmitting channel is set. Use the
same method the set the RX channel. What's more, you need to set the
thresholds of the input channels of TX and RX. Switch the menu page and press
TXThreshold and RXThreshold respectively to input the desired threshold
values.
2. Polarity Setting
Press Polarity to select "Normal" or "Invert" and the default is normal. The
oscilloscope will select the rising or falling edge as the start position during
decoding.
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8 Protocol Decoding
MSO4000/DS4000 User's Guide