RIGOL MSO/DS2000A Series - Manual (Page 183)

Chapter 8 Protocol Decoding RIGOL
MSO2000A/DS2000A User’s Guide 8-5
RS232 Decoding (Option)
RS232 serial bus consists of the transmitting data line (TX) and the receiving data
line (RX).
DeviceA DeviceB
Tx Rx
Rx Tx
Figure 8-3 RS232 Serial Bus Schematic Diagram
The industry standard of RS232 uses “Negative Logic”, namely high level is logic “0”
and low level is logic “1”.
1
0 0 0 0
1 1 1 1 1
Figure 8-4 RS232 Industrial Standard Schematic Diagram
By default, RS232 uses LSB (Least Significant Bit) transmission sequence, namely
the lowest bit of the data is transmitted first. While for MSB (Most Significant Bit),
the highest bit of the data is transmitted first.
Bit
0
Bit
5
Bit
2
Bit
3
Bit
6
Bit
1
Bit
7
Bit
4
t
Bit
7
Bit
2
Bit
5
Bit
4
Bit
1
Bit
6
Bit
0
Bit
3
t
Endian (LSB) Endian (MSB)
In RS232, you need to set the start bit, data bits, check bit (optional) and stop bit of
each frame of data.
Start Bit
Data Bit
Check Bit Stop Bit