LOOK Command
Probes signal values while the simulated circuit state is frozen.
| Command | LOOK |
|---|---|
| Abbreviation | LO |
| Category | Debugging & Analysis |
Function
The LOOK command is used to interactively probe signal values while the state of the simulated circuit is frozen in time.
Optionally, information may also be requested about the inputs to the element generating the signal (if the signal is not a primary input) and/or the loads driven by the signal.
Usage
The LOOK command is described in the Section Probing For Signal State Information in History Files.
Probing Specific Signals
The LIST keyword is used to specify the signals of interest: The command:
LOOK LIST=<signals>causes the current values of the specified signals to be reported at the terminal. The LIST keyword option is not sticky; only the values of currently specified signals are reported. For example:
>>: LOOK LIST=A
At Time= 23, Test=101:
A= '0' [Primary Input]
>>: LOOK LIST=CARRY-OUT
At Time= 23, Test=101:
CARRY-OUT= '1' [OR]The command:
LOOK LIST:produces a table of all signals states (in alphanumeric sequence). The table's format is equivalent to the PRINT (or WRITE) "dump" format, discussed in the Subsection Selecting Signals to Output in Simulation Output.
Element Input Information
For internal signals, the INPUTS keyword option causes additional information to be reported on the inputs of the elements that generate the signals. The command form is:
LOOK INPUTS:For example:
>>: LOOK INPUTS: LIST=CARRY-OUT
AT TIME= 23, TEST= 101:
CARRY-OUT= '1' [OR]
I:= AND1= '0' [AND]
I:= AND2= '1' [AND]
I:= AND3= '0' [AND]In this example, the carry-out signal is a logic-1, and it is generated by an OR gate. This gate has three inputs, and1, and2, and3, each the output of an AND gate. The second input, and2, is causing the logic-1 at carry-out.
The INPUTS keyword option is sticky; once enabled, each subsequent LOOK LIST command will also contain element input information for internal signals.The command:
NO LOOK INPUTS:removes this information from subsequent LOOK output.
Fanout Information
Fanout information can also be included in the LOOK LIST output. with the command:
LOOK OUTPUTS:For example:
>>: LOOK OUTPUTS: LIST=AND2
At Time= 23, Test= 101:
AND2= '1' [AND]
O:= CARRY-OUT [OR]additionally reports that and2 fans out to the OR gate named carry-out.
The OUTPUTS keyword option is sticky; once enabled, each subsequent LOOK LIST command will also contain the instance names of all parts driven by the traced signal. Fanout information can be subsequently removed from LOOK output with the command:
NO LOOK OUTPUTS:Displaying All Signals At A Specified State
Many times it is useful to see if there are any signals at an 'X' or 'Z' state.
To display all signals at an 'X' state, use the command:
LOOK X:Similarly, to display all signals at a 'Z' (tristate) value, issue the command:
LOOK HIZ:The format of both reports is identical to the LOOK LIST=<signals> command's report format. These two commands do not honor the INPUTS: or OUTPUTS: keyword options, if in effect.