M-1119 RIMsim Aug61

This document describes the "Read In Mode Simulator" for the PDP-1 computer, a utility routine developed primarily for maintenance and checkout purposes.

Its main function is to allow programs to be loaded into the PDP-1 without needing to activate the physical "read-in" switch. The simulator mimics the PDP-1's native read-in mode, interpreting the first three lines of a binary tape as instructions and subsequent lines as data.

Key instructions supported include:

• "deposit in-out" (dio): Stores the next three lines of data from the tape into memory.
• "jump" (jmp): Terminates the read-in mode and transfers program control to the address specified by the instruction (which occupies the last three lines on the tape).

To use the routine, operators must first load the simulator program itself into memory (e.g., via test word switches), then load the target "read-in mode tape" into the reader, and finally start the simulator routine. The document also provides details on the binary tape format, showing how instructions and data addresses are represented by hole patterns, and offers a simpler routine for general-purpose use.