Writing, Iguanas, and Electronics

Data Bus SHL Instruction

The ALU SHL instruction works on the Data Bus, and includes a source identifier, to make it easy to select the register or counter to shift. For sequential left-shifts, the OCR should be used as it will take a single clock-cycle per shift. This instruction will work on any register available on the data bus.

The Data Bus is the left or "A' side of the equation because of the Decrement and Shift-Left operations of the ALU. When performing sequential decrements or shifts, this will save a transfer operation to copy the Output Cache Register to the "A" register... the Output Cache Register can be used directly.

Usage Examples:
        Hex                Mnemonic                      Action

0CA0      ; SHL (A)            Data Bus (A) << 1 -> OCR
0CF0      ; SHL (OCR)        Data Bus (OCR) << 1 -> OCR

Updates when Executed:

  • ALU Output Cache Register
  • Carry Flag
  • Zero Flag
  • Negative Flag