Test Word
The thirty-six Test Word Switches indicate a new number for manual deposit into memory. They may also be used for insertion of constants while a program is operating by means of the operate instruction.
Sense Switches
The six Sense Switches allow the operator to manually select program options or cause a jump to another program in memory. The program can sense individual switches or the state "All Switches ZERO."
ELECTRICAL DESCRIPTION
The PDP-3 circuitry is the static type using saturating transistor flip-flops and, for the most part, transistor switch elements. The primary active elements are Micro-Alloy and Micro-Alloy-Diffused transistors. The flip-flops have built-in delay so that a logic net may be sampled and changed simultaneously.
Machine timing is performed by a delay line chain. Auxiliary delay line chains time the step counter instructions (multiply, divide, etc.). The machine is thus internally synchronous with step counter instructions being asynchronous. The machine is asynchronous for in-out operations, that is, the completion of an in-out operation initiates the following instruction.
MECHANICAL DESCRIPTION
The PDP-3 consists of two mechanical assemblies, the Console and the Equipment Frame. [Fig. 3] is a photograph of PDP-1 which is an 18 bit version of PDP-3.