The Microinstructions Dialog

The Microinstruction dialog (see Figure 24) has a table in which you can inspect and edit the parameters of existing microinstructions and in which you can add new microinstructions or delete microinstructions.


Figure 24. The dialog for editing microinstructions.

First choose the type of microinstruction you wish to inspect or edit from the popup menu at the top. To delete a microinstruction, select it in the table and then click the "Delete" button. To create a new microinstruction, click in the "New" button, at which point a new microinstruction will be added to the end of the table. To duplicate a microinstruction, select the microinstruction in the table and click the "Duplicate" button. To edit a cell, just click or double-click on it. Some cells are edited by typing new text in them, some cells are edited by selecting items from popup menus, and some cells are edited just by clicking in the check box in the cell. If you try to enter an illegal value in a cell, either the cell will become outlined in red (for example, if you type non-numeric values in a cell expecting a numeric value) or an error message will appear when you try to save the changes you made (for example, if you type in a numeric value that is out of range for that particular cell).

The columns in any of these tables can be reordered by dragging the column headers left or right to a new position. The column widths can also be adjusted by dragging the line dividing the column headers. The rows can be resorted by column by clicking in any column header.

The names of the microinstructions can contain any characters. It is strongly recommended, but not required, that all microinstructionss have unique names regardless of the type.

Clicking in the "Help" button will cause a window to appear giving you some extra (hopefully helpful) information about the current type of microinstruction being displayed.

Note that any microinstruction may be used in the fetch sequence as well as several machine instructions. Therefore, if you change the microinstruction by editing one or more of its parameters, then the change will affect the fetch sequence (if the microinstruction is used in it) as well as all machine instructions that use it. To avoid this behavior, duplicate the microinstruction, edit the duplicate, and then use the duplicate in the fetch sequence or desired machine instructions.

Comment microinstructions don't appear in this dialog box since they are essentially pseudomicroinstructions. That is, they behave differently than regular microinstructions. When executed, such a microinstruction does nothing. Instead, it is used only to add comments to microinstruction sequences. Each Comment microinstruction is unique and so you can edit its text without affecting the text in other Comment microinstructions.

The End microinstruction doesn't appear in this dialog box since it has no editable parameters.