The figure displays SPI interface analysis window, beneath it there is an image with work screen area containing the timing charts for the clock channel (SCK), select slave channel (~SS), receiving channels (MISO) and transmitting channels (MOSI). Marker 1 is set to start byte 0xAA and marker 2 is set to start of the following byte 0x55 of the channel MOSI.

The upper part of SPI windows contains an image of typical timing chart of one byte of SPI interface. Beneath it there is the panel of the main settings incident to the analyzed interface. Before you start decoding it is recommended to set the names of the interface channels on the panel "Channels" of logical analyzer. If you set the names SCK, MISO and MOSI then they automatically appear in the fields of the clock channel, receiving channel and transmitting channel.

As is known from
SPI interface specification, there are not any special signs to determine start byte, if the data are transmitted without pause and select slave signal is not used. The only way to determine start byte is to start measuring before communicating with "correct" triggering in SCK channel. As is known from SPI interface specification, SCK channel level in the standby mode (if no communication) may be both high and low. That's why to set "correct" triggering it is necessary to determine SCK level in the standby mode. To this effect it is necessary to perform the measurements several times before a long pulse/pause appears in SCK channel, which length has to differ sufficiently from adjacent pulses/pause. If a long pulse is found then SCK channel level in the standby mode is high, i.e. triggering has to go as to the falling edge if a long pause is found then SCK channel level in the standby mode is low and triggering has to go as to the rising edge. Before you start measuring it may be well to turn off the analyzed device and then press the Run button and turn on the device. If triggering is set correctly then the start of timing charts has to concur with start of communication. For the normal timing charts decoding it is necessary that the sampling frequency is 3-4 times higher than the triggering frequency.

Upon taking the timing charts it is necessary to set the values for all interface settings correctly as without it you cannot start the waveform decoding. The most common settings of SPI interface are set as default. Upon setting all the parameters it is necessary to set the marker 1 to start communication (byte).

Upon completing all such procedures you can start decoding when pressing the Decode button. Decoding results will be displayed in the table in binary and hexadecimal formats. When double clicking on the selected cell with the decoding results the marker 1 goes to start of the corresponding byte.

It is necessary to note that in addition to the timing charts decoding SPI window also allows generating the timing chart on the basis of interface settings and table data (column MOSI) for the channels SCK and MOSI, which are to be one of the logical generator channels.

It makes sense to use the flag Auto (table field autofill) only if signal generation is required.

 

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