Architecture sketch #3

The third version of the Juno architecture. The following changes have been made:

- all program visible registers have been moved to the ALU left bus.

- a temp register which will be invisible to programs has been added to the right ALU bus.

Moving the registers has greatly simplified the bus design and made the instruction set more regular and therefore hopefully less error prone to construct.

The inclusion of a temp register enables register to register operations to be implemented in microcode e.g. A = A + B can be implemented in microcode by first copying B to temp and then performing A = A + temp. This is quicker and requires fewer program instructions than writing B to memory and then adding to A.