The control logic maintains a certain amount of state for proper execution.
Halt Button HaltFF: Halt flip flop
Interrupt Button: Asynchronous button hardwired to Interrupt pin. This is for testing the interrupt functionality of the control.
Reset Button: Asynchronous button, hardwired to Reset pins.
Other internal Flip Flops and Latches:
SStepFF: 1bit FF for single stepping and button control.
IntrFF: 1bit FF for interrupt system status.
IOPEnabler: 4bit shifter (same as book).
IR.ctrl: 12bit register for controller copy of instruction.
DeviceLatch: 3bit latch for device inputs. (See ASM IOT for details).
CodeLatch: 3bit latch for display code.(See ASM DSPY for details).
Also along with the internal flip flops, we also define some internal signals which our state machine asserts however do not directly map to the pin-outs. The functionality of each of these signals is diagramed in the block diagram.
Internal Signals:
LoadLed: Force the LED latch to load.
ShowEA: Asserted when EA on bus.
ShowIR: Asserted when IR on bus.
ShowSR: Asserted when SR on bus.
LoadAC: Converted into left=1 right=1