The figure displays UART interface window,
beneath it there is an image with work screen area containing the
timing charts for the receiving channels (RxD) and transmitting
channels (TxD). Marker 1 is set to the start bytes 0x0F and marker 2 is
set to the following start byte 0xAA of the channels RxD.
The
upper part of UART window contains an image of typical timing chart of
one byte of UART 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 &qout;Channels&qout; of logical analyzer. If you set the
names RxD and TxD they automatically appear in the fields of receiving
and transmitting channels.
As is known from UART interface
specification, start bit that is always logical zero goes before the
data bit transmission, then the data bits are transmitted, at that the
low bits come first and then the parity bit can go and requisite one or
two stop bits that is always a high level. If there is not data
communication then the logical level of the corresponding channel (TxD
or RxD) will be always high. That's why it is expedient to turn on
triggering as to the falling edge in one of the channels advisably in
the same channel, where stratum bit goes first. Before you start
measuring it may be well to turn off the analyzed device and then press
the Start button and turn on the device. If triggering is set correctly
then 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 communication rate (frequency), in
rough way, rate is inversely proportional to the minimum pulse length,
e.g. for the channel RxD.
Upon taking the timing charts it is
necessary to determine the communication rate. To determine the
communication rate automatically you may press the button with
calculator icon. Communication rate is determined automatically only on
the basis of the timing chart of the channel RxD and if possible,
corrected on the basis of the standard series of speeds. Upon
determining the communication rate it may be well to set the values of
other interface settings correctly, which cannot be determined
automatically. The most common settings of UART interface are set as
default. Upon setting all the parameters it is desirable to set the
marker 1 to start bit of the channel RxD and marker 2 to start bit of
the channel TxD otherwise the first 1-3 bytes can be skipped or decoded
incorrectly.
Upon completing all such procedures you can start
decoding when pressing 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 UART window also allows
generating the timing chart on the basis of interface settings and
table data (column TxD) for the channel TxD, which has 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.