Brief Introduction to the HP Logic Analyzer
There are two principal instruments used by digital engineers to test
and debug digital systems. The oscilloscope is used in order to make
accurate timing measurements and to
investigate voltage vs. time characteristics of signals.
Oscilloscopes generally have a limited number of channels.
Logic analyzers have many more channels,
have limited timing resolution, and display only binary signals. In
the 6.111 lab we have instruments which combine logic analyzers and
digital oscilloscopes. The Model 1663AS has 32 logic analyzer
channels, the Model 1662AS has 64 channels. Both have two `scope
channels.
These logic analyzers can be configured as
timing analyzers which give a waveform display similar to that of an
oscilloscope or as state analyzers which display signals in terms of
binary or hex numbers, or both at the same time.
The logic analyzer is a fairly complex instrument. There are numerous
documents provided by HP to explain its use. At the instrument room
desk you may sign out
a Training Kit, containing
a signal source card
and a Guide with a series of tutorial lessons on how to use the instrument.
At
several places in the laboratory there is a three-ring notebook
containing the full-fledged Reference Manual.
All of this documentation, including this document, are best read in
the laboratory while you are seated in front of the logic analyzer so
that you can try out various operations as they are described.
The logic analyzers are set up and controlled by interacting with
menus. It will be much easier for you to learn the operation of the
analyzer by trying out menu selection as you go along. Indeed, you
can learn a considerable amount about the logic analyzer without
even hooking up any signals to the logic analyzer.
Turn on the logic analyzer
and wait for it to complete its
internal diagnostics and load the initial configuration.
The logic analyzer has a disk drive that can be used to store
configuration files. You will find it desirable to have your own 3.5''
DSDD (1.0 MB) disk, which is available at the instrument room.
Front Panel Controls
The front panel consists of a display, disc drive, menu buttons, key
pad, and cursor knob. There is also a mouse which can be used for
most control operations. The cursor knob is used for scrolling
through ranges of fields or for adjusting time per point, delay, etc.
The mouse, with its buttons, can be used (largely interchangeably)
with the ``Menu,'' directional arrow buttons, ``Select'' and ``Done''
buttons to select operations.
Preparing Your Own Disc
From the power-on state, click on ``Analyzer'' and select ``System,''
then click on ``RS-232/HP-IB'' and select ``Disk.'' Click on ``Load''
and select ``Format Disk.'' To proceed to formatting a disk, insert a
BLANK disk in the drive, click on ``Execute'' and ``Continue.''
Now you can ``Store'' any configuration you want to save to your disk
and at some later time ``Load'' it back into the analyzer.
There does not seem to be any simple way to initialize the logic
analyzer to its power-on state. However, if you store this state
into a file on your disc, then you can get back to the power-on state
at any time by loading the stored file. Go to the I/O menu and select
disc operations. Select the left-hand field and
then select the store operation. Now enter a name, such as
INITIAL_LD, as the destination file name and execute this operation.
Now you can reset the logic analyzer to the initial condition by
loading the file INITIAL_LD from disc.
Selecting Menus
The system configuration screen is one of several menus. The others
are easily selectable by the mouse.
To get back to the
system
configuration file from one of the other menus, select the upper
one-in-from-left field of one of these menus and then
select the desired menu.
Actually the format, trigger, and display menus
consist of a menu for each enabled analyzer. In the system
menu the initial condition is that analyzer 1 is
selected to be a timing analyzer and analyzer 2 is off. Change
Analyzer 2 to be a state analyzer. Now select the configuration menu,
and you can get either state format specification for machine 2 or
timing format specification for machine 1. You can move between these
easily using the mouse.
System Menu
Two separate analyzers can be configured. Each can be either off, a
timing analyzer, or a state analyzer.
The system menu is also used to assign pods to analyzer 1
or analyzer 2. Each pod has its own cable to a connector on the back
of the analyzer and provides sixteen channels plus a clock.
Each channel is indicated by a dash or an up-down arrow.
The up-down arrow
indicates that transitions on that signal are occurring.
Format Menu
The primary use of the format menu is to enter labels and assign
individual signal(s) to those labels. You can turn a label on or off
or modify it, which means that you can enter new text for that label.
In this menu you can also select a threshold which is used to
determine whether the pod signal is 1 or 0. Almost all of the time
you will keep the default threshold set for TTL. When in the state
format menu you can also select the clock which will be used to sample
the pod signals for each state. There is one clock signal for each
pod. They are labeled J, K, L, and M for pods 1 through 4
respectively. You can enable the sampling of data on the falling,
rising , or both edges of the clock, or when it is low or high. If
you select multiple clocks, then the state will be sampled when either
of the selected conditions is satisfied. You can even select clocks
which are wired to pods which are not assigned to this state analyzer.
If you have both analyzers as
state analyzers you can use one clock to clock the lower eight bits
and another to clock the upper eight bits. Details are given in
Chapter 11 of the Reference Manual.
Trigger Menu
As with the format menu, there are two types: the timing trigger
specification and the state trigger specification. The basic function
of both of these menus
is to decide what information to store and when to stop storing
information and switch to the display menu. Both of these menus can
be set to capture a single set of data or to repetitively capture and
display data. The term ``to arm'' means that when the arm condition
has occurred, the analyzer starts looking for the trigger condition.
Most of the time, the arming is accomplished by pushing the run
button.
Sometimes an analyzer may be armed by the other analyzer.
The method of specifying the trigger condition is different for timing
and state analyzers. A timing analyzer triggers after encountering a
selected pattern and then a selected edge of one or more signals. You
can specify a constraint that the specified pattern must be present
for
> some time period or < some time period.
If you have selected that the pattern be present for >, then you can
trigger on an edge. The edge trigger can be falling, rising, or
either edge of one or more signals. If you set the base to binary,
then the normal display clearly shows which edges cause the trigger.
If you set the base to hex, then you will see a $ sign to indicate
that some trigger is specified for that hex digit. If you have
selected
<, then the logic analyzer triggers whenever the specified pattern
has existed for less than the specified time period. If you set the
acquisition mode to glitch and select >, then you can specify
the trigger to occur on the OR of edges or a glitch.
A glitch is any transition crossing the logic threshold more than once
between samples. The logic analyzer is not guaranteed to detect
glitches which are less than 5 ns wide. In glitch acquisition mode,
the amount of data that can be stored is reduced, as half the memory is
used for storing the data samples and the other half for storing the
second transition of a glitch in a sample.
State Trigger Menu
The state trigger menu is organized somewhat differently but serves the
same function of specifying when the logic analyzer is to trigger. It
also specifies the states that are to be stored before and after
triggering. Rather complicated sequences can be specified. When the
state analyzer is used to debug software running on a microprocessor
or a microsequencer, the logic analyzer can be set to look for the nth
entry to a particular subroutine and then the nth entry of a
subroutine called within that subroutine.
This can be continued for up to eight levels.
A complete description of the state
trigger specification menu is given in
chapter 12 of the
Reference Manual.
Display Menus
The display can be of waveforms or listings for either
type of logic analyzer selected. In the waveform display,
you can set the time/div and the trigger; and the
display looks much like a multi-trace oscilloscope. If you select the
markers field, you can turn them Off or turn them to indicate Time.
You then can control
the position of the X and O markers, and the time
difference between these markers and between the markers and the
trigger will be displayed.
In the listing display, the sample number is displayed in the
left-hand column with the sampled signals in the remaining columns.
You can use the knob to scroll
this information up or down. You can also move to any position by
entering the number of the data sample. If you wish, you can use the markers
and have them placed on specified patterns for easy identification of
events. For more information on use of the markers, see pages
13-4 through 13-11 and 14-12 through 14-20 in the Reference
Manual.
You can switch the type of analyzer between state and timing without changing anything else and re-acquire the data if you wish to go between waveform and state displays. If you have two analyzers enabled, one as a timing analyzer and one as a state analyzer, there is a third mixed mode display which allows you to see both timing and state information.