(TD) 1.2 Set the Base and Dispaly Time Unit

The base time unit controls the accuracy of the of time calculations. It is the smallest representable amount of time, and all time values are internally stored in terms of the base time unit. The display time unit controls the units for entering and displaying the results. At the beginning of a new design you should check these settings to make sure they are valid for the time ranges that you are working in.

Set the Base Time Unit:

The base time unit for your project should be set at least one unit below the units you are working in for best rounding performance during division operations (clock frequencies are inverted and stored internally as clock periods). The circuit that we are modeling in this tutorial has gate propagation times in the range of 3 to 18 nanoseconds and a clock with a period of 20ns. Therefore we will set the base time units to picoseconds.

•Select the Options > Base Time Unit menu, to open the Base Time Unit dialog.

•Check the Active Diagram box so that the dialog operates on your new timing diagram. Notice that the dialog displays the name of the diagram so that you can tell which diagram is the active one in a multi-diagram display.

•Check the ps button to set the base time unit to picoseconds.

•The remaining options control how any existing parameters or signals are changed when the base time unit is changed and have no effect on an empty timing diagram.

•Press the OK button to close the dialog.

td1_baseTimeUnitDlg

Set the Display Time Unit:

Set the display time unit to the units you most commonly use in the design. In this tutorial, all of the times are listed in nanoseconds so that will be the easiest time setting to enter the values.

•Select the Options > Display Unit menu option. This will display a submenu of display time units. The checked time is the current display time unit (Default is ns = nanoseconds).

•Click on ns to make nanoseconds the display time unit.

td1_displayTimeUnitMenu