ppb Address 6

MANUAL CONTROLS

The Console of PDP-3 has controls and indicators for the use of the
operator. Fig. 4 is a close-up of the control panel of PDP-1, the 18 bit
version of PDP-3. All computer flip-flops have indicator lights on the
Console. These indicators are primarily for use when the machine has
stopped or when the machine is being operated one step at a time. While
the machine is running, the brightness of an indicator bears some
relationship to the relative duty factor of that particular flip-flop.

Three registers of toggle switches are available on the Console. These
are the Test Address (15 bits), the Test Word (36 bits), and the Sense
Switches (6 bits). The first two are used in conjunction with the
operating push buttons. The Sense Switches are present for manual
intervention. The use of these switches is determined by the program
(see System Block Diagram and Skip Group Instructions).

Operating Push Buttons

_Start_ - When this switch is operated, the computer will start. The
first instruction comes from the memory location indicated in the Test
Address Switches.

_Stop_ - The computer will come to a halt at the completion of the
current memory cycle.

_Continue_ - The computer will resume operation starting at the state
indicated by the lights.

_Examine_ - The contents of the memory register indicated in the Test
Address will be displayed in the Accumulator and the Memory Buffer
lights.

_Deposit_ - The word selected by the Test Word Switches will be put in
the memory location indicated by the Test Address Switches.

_Read-In_ - When this switch is operated, the photoelectric paper tape
reader will start operating in the Read-In mode. (see Input-Output).

In addition to the operating push buttons, there are several separate
toggle switches.

_Single Cycle Switch_ - When the Single Cycle Switch is on, the computer
will halt at the completion of each memory cycle. This switch is
particularly useful in debugging programs. Repeated operation of the
Continue Switch button will step the program one cycle at a time. The
programmer is thus able to examine the machine states at each step.

_Test Switch_ - When the Test Switch is on, the computer will perform
the instruction indicated in the Test Address location. It will repeat
this instruction either at the normal speed rate or at a single cycle
rate if the Single Cycle Switch is up. This switch is primarily useful
for maintenance