Configuring the Logic Analyzer
The LAX instrument can be configured after placement on the schematic sheet. Simply right-click over the schematic symbol for the instrument and choose the Configure command from the bottom of the pop-up menu that appears (e.g. Configure U2 (LAX) for a logic analyzer with designator U2). Alternatively, click on the Configure button available in the Component Properties dialog for the instrument.
Use the dialog to configure the device as required. Upon clicking OK, the schematic symbol will dynamically update to reflect your configuration choices.
The following sections discuss the various configuration options available.
Capture Width
Use this field of the dialog to determine how many signal channels each defined signal set will contain. Set the width to be either 8, 16, 32 or 64.
Memory Size
Use this field to choose between predefined internal storage memory (1K, 2K or 4K) or specify the use of external memory.
Connecting to External Memory
By choosing ExternalMemory for the Memory Size opjtion, an external memory interface will be added to the instrument's schematic symbol - allowing you to connect your own external memory, which can be either synchronous or asynchronous.
The external RAM data width is equal to the number of input channels supported by the instrument (specified by the Capture Width option). The size of the capture buffer organized in the external RAM block used is defined as:
Sample buffer size = 2Memsize
where Memsize equals the size, in bits, of the physically connected memory address bus.
The maximum supported memory address bus size is 20 bits, allowing a maximum sample buffer size of 1024K.
Whatever size block of RAM you use, the value for the memory address bus width must be entered into the Ext Mem Addr Width field of the Configure Logic Analyzer dialog.
Configuring the Signals to be Captured
Signals are fed into the instrument as grouped sets. Up to 16 sets can be defined and each set will contain n signal channels (n=8, 16, 32 or 64) in accordance with the defined Capture Width for the instrument. Use the Signal Sets region of the Configure (Logic Analyzer) dialog, to define sets of signals as required.
By default, a single signal set will exist when the LAX instrument is first placed. This set - Signal Set 0 - will contain no specifically defined signals, but will provide an input based on the supported channels configured for the device. This input will have the default name Set0_Sparen-1..0, where n is the Capture Width. The figure above shows the default signal set for a placed LAX instrument, configured with a Capture Width of 16.
The default signal set cannot be deleted. If you try to delete it, on exiting the dialog a new default signal set will be created, complete with original default naming.
Adding Signal Sets
As mentioned previously, up to 16 signal sets may be defined for a LAX instrument. This means you are not restricted to monitoring only a set number of channels - i.e. without the notion of sets, a LAX with Capture Width = 16 would only ever be able to monitor a maximum of 16 unique input signals. Sets give you the freedom to hook up any number of net and bus signals to the Analyzer and provides the ability to capture data for a nominated set while the circuit is under test - no having to rewire, recompile, build and download the design to the target physical device each time you want to change the signals that you wish to monitor! The configurable LAX instrument also allows you to trigger off any defined signal set, while capturing data from that same, or different set - giving maximum flexibility.
To define additional signal sets for the instrument, simply click on the Add Signal Set button, or use the Alt+S keyboard shortcut. Give each new set a meaningful name, or accept the default naming (Signal Set 1, Signal Set 2, etc). An input interface will be created on the schematic symbol for each set defined. To remove a defined signal set, simply select the set in the list and either click the Remove button or use the Alt+R shortcut.
Changing Interface Ordering
After defining the signal sets, you may find that you want to change the order in which their corresponding interfaces appear on the LAX's schematic symbol. Support for interface reordering is provided through two additional buttons in the dialog
- Move Up and Move Down. Alternatively, you can simply click on a signal set entry in the list and drag it to the required position.
Adding Signals to a Set
When a set is added, a single bus input is defined by default, the width of which is equal to the Capture Width specified for the instrument. If you are simply monitoring a bus of the same width, you could accept and wire to this default input. A more typical scenario will be that you wish to monitor various nets and buses from around the circuit. In order to connect these various signals to the instrument, you must further refine the interface for a signal set, by defining a distinct input for each net and bus signal you wish to monitor using that set. Each of these inputs is added to the parent signal set as a signal.
To add a signal to a signal set, simply select that set in the list and either click the Add Signal button or use the Alt+A keyboard shortcut. The new signal will be added as an entry under the signal set. Give the signal a meaningful name - typically the actual name of the signal you are monitoring. If the intended input is a bus signal, specify the index as part of the name, for example DATA_IN
[7..0].
You can add as many signals to a set as you like, provided the number of channels for that set is not exceeded. Remember, the number of channels per signal set is equal to the Capture Width defined for the instrument. Consider for example a LAX instrument with a Capture Width of 32, the channel allowance for a set is 32 and could be assigned as follows:
- 2, 8-bit bus signals
- 2, 4-bit bus signals (nibbles)
- 8 single net signals.
Any channels not assigned for specific signals will appear in the interface for that set as:
Setx_Spare(y - 1) - z..0,
where:
x is the set number
y is the Capture Width for the instrument
z is the number of channels already used.
Although the default 'spare channels' signal is not available in the dialog for editing, you can simply add a signal that caters for these remaining channels, allowing you to use a more meaningful name (such as UNUSED). It is good practice to tie any unused channel inputs to ground.
To remove a defined signal, simply select the signal in the list and either click the Remove button or use the Alt+R shortcut.
You can change the order of signals within a set using the Move Up and Move Down buttons. Alternatively, you can click on a signal and drag it to the required position - either within the same set, or to another defined set.
Using Net Labels to Create Signals
To expedite the configuration process, you can select net labels on a schematic and then use the Paste button in the Configure (Logic Analyzer) dialog - signals with the corresponding names will be added to the currently selected signal set.