Master Clear

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The MCL (Master Clear) button is used to force the computer into a defined initial state. The CPU loads the microprogram into the control store from the EPROM where it is stored. The microprogram then traps to the master clear routine. This initialization is also performed when the CPU goes through the power up sequence, and when the bus line (negative logic) BMCL is activated.

Note: the MACL command in OPCOM performs the same initialization, but does not reload the control store.

Master clear routine

The master clear routine turns off running indicator, the PIE register is cleared. The paging and interrupt systems are turned off. The paging system is set in "normal" mode (as if the REX instruction had been executed). The CPU self-test routine microprogram is executed. If no errors are found, the running indicator lamp is lit, and the terminal interface on the CPU board (terminal no. 1) is initialized to 7-bit plus even parity. Parity is not checked on input.

When the master clear routine is finished, the CPU will be in STOP mode.