The fetch sequence dialog box (see Figure 22) lists on the left side (under "implementation") the current sequence of microinstructions forming the fetch sequence.
Figure 22. The fetch sequence dialog.
If you wish to delete one of the microinstructions from the sequence, select it by clicking on it. Then click the »delete button. If you wish to insert a new microinstruction in the sequence, select the microinstruction you want from the list in the right part of the dialog box and then select in the list on the left side of the dialog box the microinstruction before which you wish to insert the new microinstruction. Now click on the «insert« button. If you want to add the new microinstruction to the end of the fetch sequence then don't select any microinstruction in the list on the left before clicking the «insert« button. To reorder the microinstructions in the fetch sequence, just drag them up or down in the list on the left side of the dialog box.
At the bottom of the list of all microinstructions on the right (not shown in Figure 21), there is a microinstruction named "Comment". When executed, this microinstruction does nothing. Instead, this microinstruction plays the role of a comment in the fetch sequence's implementation. To add a Comment micro to the fetch sequence, first select it and then press «insert«. A new Comment microinstruction is added to the implementation. You can now edit the comment in the implementation list by double-clicking it (or pressing F2). Comments are colored gray and use an italics font to distinguish them from regular microinstructions.
Note: Every fetch sequence needs a Decode microinstruction in its implementation. The Decode microinstruction causes CPU Sim to decode the fetched instruction and begin executing the microinstructions in its execute sequence.