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Entry Swithes: just another register

10/19/2009

Here is a simple idea, so simple that I still wonder why it didn't occur to me before: The Entry Switches are nothing but another register within the CPU.

For "normal" registers, I have a set of lamps and buttons on the Console to select one register at the time, show its content as well as it's control signals status and also to CLEAR, LOAD, INC, DEC and open its buffers to either the internal Data Bus or the Address Bus. Well, if Entry Switches are another register, then it must be present in that buttons/lamps set.


Thus, I will simply add another button labeled "SW"... (in place of the "MB" wich is not longer needed).

By pressing that button, the operator selects the Entry Switches for watching its content in the lamps. He also will be able to dump its content to the Data Bus (button "OTD") or to the Address Bus (OTA) as with any other register.

For example, if I want to load the IR register from the Entry Switches, I press the "SW" button, enter the desired content in the switches, then I press the "OTD" button so the content is available to the internal Data Bus; then I select the IR register by pressing the "IR" button and then press the "LD" button to load that register from the Data Bus.

That is when the computer is in "Debug Mode". In "Programming Mode", the Entry Switches behavior will be totally different. In Programming Mode, the operator needs to be able to examine and/or alter memory content and to run a program starting in a given (by switches) memory address. But that is an old story, I mean, I had conceived that part before.