User Manual

7 Protocol Decoding RIGOL
DS4000 User’s Guide
7-5
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
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
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.
bit0 bit1 bit2 bit3 bit4 bit5 bit6 bit7
t
bit7 bit6 bit5 bit4 bit3 bit2 bit1 bit0
t
Endian (LSB) Endian (MSB)
In RS232, baud rate is used to represent the transmitting rate (namely bits per
second) of the data. The commonly used baud rates include 4800bps, 9600bps,
19200bps, 38400bps, 57600bps and 115200bps.
In RS232, you need to set the start bit, data bits, check bit (optional) and stop bit of
each frame of data.