This is the hardware decoding unit. When activated, this unit decodes the conventional instruction in the Instruction Register, setting the Micro Program Counter; it writes to the X12, X11, Lo8 registers simultaneously.
To show the Microprogram window, click here; you cannot show the window if no document is open.
The Control Store contains the entire microprogram, which endlessly fetches, decodes and executes instructions from the main memory.
To show the Register window, click here.
The registers are a scratchpad memory; the processor can access their data very quickly. While the processor is running, the (writable) registers can be set via the C bus, which may carry the shifter output.
The Micro Instruction Register contains the last microinstruction extracted from the Control Store. Its fields control many parts of the processor.
The Micro Sequencing Logic decides whether to take a jump (in the microprogram) or not. The decision is based upon the Negative and Zero flags, and the “Cond” field of the Micro Instruction Register.
To modify the value stored in the Arithmetic Logical Unit, click here.
This unit performs the basic calculations (add, logical “and” and one’s complement) and sets the Negative and Zero flags, according to its contents.
To modify the value stored in the Micro Program Counter, click here.
This register points to the microinstruction currently executing.
To modify the value stored in the M multiplexer, click here.
This multiplexer controls the input to the Micro Program Counter. A jump in the microprogram results in feeding the Micro Program Counter with the “Addr” field of the Micro Instruction Register.
To modify the value stored in the Incrementer, click here.
The incrementer provides the standard advancing of the Micro Program Counter.
To modify the value stored in the Shifter, click here.
The Arithmetic Logical Unit feeds the shifter with its result. If the C bus is not disabled, its contents go to the Registers scratchpad.
To modify the value stored in the A multiplexer, click here.
This multiplexer controls the left input to the Arithmetic Logical Unit. It chooses between the A latch and the Memory Buffer Register.
To modify the value stored in the Memory Buffer Register, click here.
When this register is active, the Shifter feeds it. Here the processor keeps values read from and to be written to the main memory.
To modify the value stored in the Memory Address Register, click here.
When this register is active, the B latch feeds it. When the processor needs to read from or write to a main memory address, it puts here the memory address.
To modify the value stored in the B latch, click here.
The register addressed by the “B” field in the Micro Instruction Register feeds the B bus, which in turn feeds the B latch.
To modify the value stored in the A latch, click here.
The register addressed by the “A” field in the Micro Instruction Register feeds the A bus, which in turn feeds the A latch.
