Method and apparatus for selecting and displaying a high resolution window from a main display

• US 4,975,636 A
• Filed: 05/01/1989
• Issued: 12/04/1990
• Est. Priority Date: 05/01/1989
• Status: Expired due to Term

• Current Assignee: Agilent Technologies, Inc.
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Desautels, Patricia A.
• Primary Examiner(s): Karlsen, Ernest F.
• Application Number:
  US07/345,903
• Time in Patent Office: 582 Days
• Field of Search: 324/121 R, 324/77 R, 340/723, 340/728, 364/487
• US Class Current: 324/121.00R
• CPC Class Codes: G01R 13/24 Time-base deflection circuits

Abstract

A windowed portion of a displayed waveform under test, typically from an oscilloscope display, is simultaneously displayed at a higher resolution by using a software program in conjunction with the existing timebase circuit rather than using a second timebase circuit. The software uses the resolution of the interpolators (a stretcher circuit which uses capacitors to hold acquire a charge and measure the amount of time necessary to slowly discharge the circuit) to carry through all the plotting of points to a first and second display.

Claims

1. A method of concurrently displaying a repetitive waveform under test on a first display at a first resolution and user-defined subsection of the waveform under test at a second resolution higher than the first resolution on a second display, comprising the steps of:

initializing hardware;

determining the display left edge residual time and the high resolution column increment from the user-defined information and the sample time;

making an acquisition of a set of points relative to a trigger event and storing the set in a memory;

calculating a high resolution column index from the residual time and the interpolater time and the high resolution column increment for each point to be displayed on the first display;

truncating a value equal to the high resolution column index to determine the appropriate column value for each point to be displayed;

plotting each point to the first display according to the column value for the time axis and the value stored in memory for the y-axis;

testing each point to determine if it lies within a user-defined subsection of first display;

subtracting the left subsection marker value from the high resolution column index to obtain a second display column value for each point within the user-defined subsection of the first display;

multiplying the second display column value by the expansion ratio of the first display to the second display for each point within the user-defined subsection of the first display;

converting the second display column value to a column measurement and truncating it to determine the appropriate second display column;

plotting each point within the user-defined subsection of the first display to the second display according to the second display column value for the time axis and the value stored in memory for the y-axis;

repeating the acquisition step and succeeding steps until halted by a user command.

2. An apparatus for concurrently displaying a repetitive waveform under test on a first display at a first resolution and a user-defined subsection of the waveform under test at a second resolution higher than the first resolution on a second display, comprising:

sampler means for continuously sampling and holding the analog value of the waveform under test upon user command;

converter means for converting each sampled signal from the analog value to a digital value;

first memory means for continuously holding the last N sampled signal where N is the number of location within the first memory means;

sample clock means for clocking the sampler means and the converter means;

processor means for converting digital signals from the first memory means into display signals for a first display having a first resolution and for a second user-determined display having a second resolution higher than the first resolution;

display memory means for holding display signals;

display means for displaying signal according to display signals in the display memory; and

timebase means connected to the processor means and the sample clock means for controlling the sampling, converting, and storing of samples, and for measuring the time between a user-defined trigger event and the next sample clock pulse.