Front Panel and Display Leds

 

The front panel includes all of the necessary buttons for PDP-8 compatibility. The board includes two banks of 16 leds. One of these banks is wired directly to the bus of the PD-PP so we can monitor all actions on the bus. The second bank is connected to latched values from the bus. This bank displays the contents of registers when they come across the bus and is set with the Display pushbutton.

• Switch Register.
• Function Code. Used byDisplayandExecute.
• Execute. Execute a basic load operation determined by the code switches.
• Display. Display a datapath register onto the latched leds.
• Single Step. Perform a single instruction cycle.
• Manual Execution. Execute current IR instruction, skipping the fetch cycle).
• Continue. Continue uninterrupted execution.
• Halt. Halt the machine and go into idle state.
• Reset. Asynchronous reset.
• Interrupt. Force an interrupt.

The Execute and Display buttons use the three function code switches to determine what registers to load or display. For Execute, the code switches determine which register to load with the value of the switch register provided.

Furthermore, the display codes set which register to maintain on the latched Leds. The function codes determine which registers to display.