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Step Execution

To run a program is Step Mode, activate the STEP switch (up). In this mode, only one instruction is fetched and executed at a time after which the machine falls into Halt mode automatically. You run the next instruction by pressing the CONT button.

Normally, you stop the machine (by pressing the HALT button) before activating the STEP switch, but you can also activate the switch directly while the computer is still running. In that case, the machine will let the current instruction to finish, then will fall into Halt mode.

Step Mode is useful for debugging developing programs. Say for instance that your program crashes. What you do is to enter Step Mode as explained; for each step (while in Halt mode), you possibly examine different registers and memory contents in order to figure out what the problem is.

As said, you can press the CONT button to execute the next instruction. In that case the program will continue from the point it was left with total independence of the A-DISP reading. This implies that, between steps, you can freely explore the memory by using the Entry Section of the Console; the execution of each step, however, will update A-DISP and D-DISP as it does for normal execution.

You can also run the next instruction from any given point in memory by pressing the START button instead. When you do that, the program counter (PC) is loaded with the content shown by the A-DISP. Thus, in order to execute from a given address, you enter that address in the Entry Switches, press the LOAD button, then the START button.

You can leave Step Mode at any time by putting the STEP switch down again. When you do that, the machine is must likely in Halt mode so you will possibly need to press the START or CONT button to resume normal execution.