Cleverscope CS300 - Using the Protocol Decoder - Additional Notes; C Protocol Example

Cleverscope CS300 Reference Manual v2.11
Page 146 www.cleverscope.com ©Cleverscope 2004-2015
21.6 Using the Protocol Decoder - Additional Notes
The I
2
C decoder uses colour highlighting to show the address, data, start, stop, ack, and fault/non fault status.
The protocol decoder works over both regular captures (automatically improving sample resolution if required),
and over full buffer transfers. A full buffer (4M) capture of 2 seconds will have 500ns resolution, still sufficient
to decode 400 kHz I2C, 115 kbaud serial, and 500 kHz SPI. 2 seconds of transfer represents a message of about
100,000 I
2
C characters, 23,000 serial characters or 125,000 SPI characters if transmitted at full rate.
Decoded messages are automatically saved in the .apc file when saved, allowing the captured signal and
decoded message to be viewed using the Cleverscope application – useful for sharing via a network, email or
later review.
If the display width chosen on the Scope Display results in a resolution that doesn’t show the individual bits of
the signal then the protocol cannot be decoded or displayed. However, clicking Get Frame should be able to
decode it because the data will be brought in at a higher resolution.
In addition the decoders work on a frame by frame basis. The current frame is set using Current Frame on the
Cleverscope Control Panel. Changing the current frame allows reliable navigation and display of each frame
contents.
If the protocol decoder is enabled, as each new frame is displayed for the first time, the frame is decoded, and
optionally added to the Notes. This capability means that multiple short messages can be captured and
displayed and decoded, without capturing the intervening dead space.
For example to record the first 50 messages being sent, set the number of frames to at least 51, and the number
of frames per capture to 50. (Use Acquisition Settings on the Settings menu).
Click Single (assuming you have set up the trigger beforehand), and the next 50 messages will be captured.
You can now use Current Frame to navigate each message. As the frame is loaded, it is decoded, and the
message added to Notes, if Copy to Notes is enabled.
Inter message time can be as short as 20us.
21.7 I
2
C protocol Example
Cleverscope’s built-in I
2
C protocol analyser simplifies signal stream analysis of the two-wire multi-master bus
typically used to communicate between peripherals and embedded devices
Setting up the I
2
C protocol analyser
The setup screen shows the I
2
C decode selected in the Protocol List and the settings on the Protocol Options tab
as below: