When
testing any digital device you may need to analyze the data
communication channel, if any. At first sight this trivial task such as
to take the timing charts from the necessary communication channel
lines, determine the interface type and manually decode the taken
timing charts, does not look like complex. But upon making some
attempts to decode the timing chart you will not obviously want to
perform this routine procedure that much. To set about decoding it is
necessary at least to become familiar with specification of the
analyzed interface and master its timing chart formats. It will take
much time, especially when you have not any normal interface
description within reach. Upon familiarizing with the interface you
will know that the most interesting thing is decoding. Generally,
in most of interfaces there are some signs of bytes transmission start
and end, except for SPI,
when the data are transmitted without any delay. That's why decoding
starts with the signs searching. Upon finding, e.g. the start
transmission sign, one start decoding the data and a lot of questions
arise about particularities of the analyzed protocol that require
examining the specification of the analyzed interface, comparing the
timing charts with their analogs in specification. It can take your
time; divert you from other and probably more interesting tasks. We can
exemplify from experience about time expenditure for the interface
timing charts decoding I2C
(used in video capture board), when manually decoding for three and a
half hours we managed to allot even 48 bytes, at that all obtained
information was thoroughly recorded on a paper subject to any error.
When decoding the same interface with analogous program (subsequent
pilot model of logical analyzer) the whole communication cycle of 1026
bytes long was analyzed for 8 minutes but it took one and a half day to
write the analysis program.
It does not mean that without any
preliminary preparation one can decode the data of any interface by
pressing a couple of buttons for several minutes. In any case before to
analyze the selected interface it is strictly recommended to read its
specification as no program can help you without comprehension of
interface operation principles.