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Operational Modes

The LC-81 minicomputer operates in two distinct modes: Halt and Run.

After power-on or reset, the machine falls into HALT mode. This is accomplished by asserting a BUSREQ to the microprocessor. Since the Console Controller does not depend on software to operate (except for the START button) it can take control of the buses (both internal and external) so this is the time for the Operator to make use of the Console for inspecting/changing memory content (both private and external) as well as peripheral registers.

Pressing the START or CONT button causes the machine to enter RUN mode. This is accomplished by removing the BUSREQ to the microprocessor so it can resume execution. The Operator can stop the machine at any further time by pressing the HLT button which causes the machine to enter HALT mode again.

STEP execution is also supported. This is accomplished by synchronizing with the microprocessor signal M1 which activates at the beginning of each Opcode Fetch cycle.