Chapter 6 Protocol Decoding; Rs232 Decode (Optional) - UNI-T UPO3000E Series User Manual

Chapter 6 Protocol Decoding

UPO3000E decodes the input signals of the analog channels using common
protocols, including parallel, RS232, I2C, SPI, CAN, LIN, and FlexRay. Users
can easily find errors, debug hardware, and speed up development progress
by protocol decoding, which provides guarantees for completing projects with
high speed and high quality.
6.1 RS232 Decoding (Optional)
RS232 interface is the standard asynchronous transmission interface
established by Electronic Industries Association. Normally, there are two
application types: DB-9 and DB-25, it is suitable for data transmission rate
between 0 to 20000b/s, which are widely used in PC communication interface.
According to the protocol, the data will be combined to form a group of
specific serial bits, and sent out using asynchronous serial method. The data
sent each time is composed according to the following rules: a start bit is
sent first, followed by 5~8 data bits, then an optional parity bit, and finally
1 or 2 stop bits. The data bits size should be decided by the two communication
parties, which can be chosen between 5 to 8 data bits; there may be no
parity bits, or the odd parity or even parity can be selected; and the stop bit
can be 1 bit or 2 bits. In the following instruction, a data string transmission
is called one frame, shown in the figure below:
RS232 Selection:
Press DECODE type, and select RS232 by the Multipurpose knob. You
can also switch the trigger type by consecutively pressing the type key, then
press the Multipurpose knob to confirm.
Source:
Press the source key to select the trigger source, you can select CH1, CH2,
CH3, or CH4. The currently selected source is displayed at the upper right
corner of the screen.
Note: Only selecting the channel with connected signals as a trigger source
can obtain a steady trigger and correct decoding.
Polarity:
Press the polarity key to choose the trigger polarity: Positive polarity or negative
polarity.
(1) Negative polarity: Opposite logic level polarity, i.e. high level is 0, low
level is 1.
(2) Positive polarity: Normal logic level polarity , i.e. high level is 1, low level
is 0.
Baud Rate:
RS232 communication is an asynchronous transmission communication
without clock signals during the data transmission process. In order to solve
the data bit problems, the protocol specifies that both communication parties
need to agree on the baud rate. Normally, the baud rate is defined as bits
transmitted within 1 second. For example, 9600bps means that 9600 bits
can be transmitted within 1 second. Note that the start bit, data bit, parity
bit and stop bit are all regarded as bits. Therefore, baud rate is not directly
equal to valid data transmission rate. The oscilloscope will sample the Bit
value according to the set baud rate.
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