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Control Panel sequences

10/19/2009

When the computer is in Programming Mode, the Control Panel needs to run sequences for reading and writing from/to Main Memory.

The Heritage/1 is a sequential synchronous machine. This means two things: (1) every data transfer within the machine is synchronous with respect to a central Clock (signal CLK), and (2) sequences are synchronous with respect to a central Counter (signals ET0, ET1).

The Control Panel is an exception to this rule when the machine is in Debug or Programming mode. That is because the Control Panel must be the "ultimate resource" when things go wrong, so it cannot rely on any circuit (such as IDS) used for normal operations that, because of its complexity, is more suitable for failures that the Control Panel itself.

This is one reason. The other is the nature of "modes" in the Heritage/1. Debug or Programming modes apply when the computer is in Halt. In that condition, the Time Counter (T-Counter) is frozen at T1 (ET0=ET1=0) which warranties controllers (others than the Control Panel) can not run any sequence. When the computer is in Halt condition, only the Control Panel can take control, so the most natural thing is that it utilize independent means for producing the sequences it require.