This menu is used to call up dialog boxes for the purpose of changing the components of the current machine (see Figure 12).
Figure 12. The Modify menu.
Machine Instructions...
Choosing "Machine Instructions..." from the Modify menu brings up the machine instruction dialog in which you can modify machine instructions.
Microinstructions...
Choosing "Microinstructions..." from the Modify menu brings up the microinstruction dialog in which you can modify the microinstructions.
Hardware modules...
Choosing "Hardware modules..." from the Modify menu brings up the hardware modules dialog in which you can modify the hardware modules (the registers, register arrays, condition bits, and RAMs) of the current machine.
Fetch Sequence...
Choosing "Fetch Sequence..." from the Modify menu brings up the fetch sequence dialog in which you can modify the fetch sequence.
EQU's...
Choosing "EQU's..." from the Modify menu brings up the EQU dialog in which you can modify the global EQUs.
General Notes
The Modify menu is disabled when CPU Sim is in debug mode (that is, when the "Debug Mode" menu item is checked in the Execute menu).
All of the dialog boxes mentioned above except the fetch sequence dialog display a table in which you can inspect and edit the parameters of existing components and in which you can add new components or delete components, as illustrated in the tutorial on creating new machines. To delete a component displayed in the dialog box, select it in the table and then click the "Delete" button. To create a new component, click in the "New" button, at which point a new component will be added to the table. 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 columns. The rows can be resorted by column by clicking in any column header.
Help buttons
Almost every dialog box in which parts of the machine can be modified contain a button labeled "Help". (On Macintosh computers, it might appear as a circle containing a question mark.) Clicking in the "Help" button causes the appropriate window from the online help to appear giving you some extra (hopefully helpful) information about the current dialog box.
Editing Microinstructions from the Fetch Sequence or Machine Instruction Dialogs
It is often the case that, when you are modifying the fetch sequence or the machine instructions, you will find that you need to modify or create a new microinstruction. The easiest way to do so is to double-click on the list of current microinstructions on the right side of the dialog box, which will bring up the dialog for editing microinstructions. When you are finished editing the microinstructions, you can close that dialog box and can resume editing the fetch sequence or the machine instructions. Important note: Any changes that you make to microinstructions are applied to the current machine, even if you cancel any changes to the fetch sequence or machine instructions.