The figure displays 1-Wire
interface analysis window, beneath it there is an image with work
screen area containing the timing chart of data channel (DQ), at that
the measurement was performed at Fs =200 KHz but the figure displays
the timing chart for Fs =50 KHz. Marker 1 is set to start reset pulse
and the marker 2 is set to start bytes transmission 0xСС.
The
upper part of 1-Wire windows contains an image of typical timing chart
of 1-Wire interface. As in the timing chart the red lines imply that
bus is moved to logical zero by master, blue ones - by slave and gray
ones imply that the bus is moved to logical item by raising resistor.
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 name DQ, then it automatically appears in the
field of data channel.
As is known from 1-Wire interface specification,
the session starts when master sets the reset signal (low level of more
than 480 mcs long) and then confirmation signal is set in 15-60 mcs
(low level of 15-60 mcs long) if there is only one slave in the bus.
Upon receiving the confirmation signal the master transmits one or more
bytes, at that the high-order bits go first, slave responses master as
required. As the session starts when DQ line goes from high to low
logical level then it is expedient to turn on triggering as to the
falling edge. 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 the start of timing chart has to
concur with start of communication. For the normal timing charts
decoding it is necessary that the sampling frequency is at least 200
KHz.
Upon taking the timing charts it is desirable to set the
marker 1 to reset signal otherwise the nearest reset signal right to
the marker 1 will be searched and then one session may be skipped. For
detailed decoding and description of transmitted bytes you can select
one of the standard devices supporting 1-Wire interface, of course if
its instruction set is in agreement with the instruction set of
analyzed device. There is only one type of devices - thermometers
DS18x20/DS18x22 in the dropdown list that can be subsequently added by
other devices.
Upon completing all such procedures you can start
decoding when pressing the Decode button. Decoding results will be
displayed in the table in hexadecimal format (Code) except for start
and confirmation signal and in character format (Description). When
double clicking on the selected cell with the decoding results the
marker 1 goes to start of the corresponding element of 1-Wire interface.