M-1117 TC-FRAP Jul61

This Permanent Memorandum, dated July 31, 1961, describes TC-FRAP (Type Controlled - FRAP), a system for preparing and debugging symbolic (assembly) programs using an on-line typewriter.

TC-FRAP enables programmers to type in symbolic code, which is then processed by the FRAP assembler to punch a read-in mode tape. A core feature is its comprehensive error correction: mistakes can be corrected both during the initial typing process and after a program's first pass through the assembler. The typewriter provides complete control over the assembly process.

The system includes a Main Control loop for general program management, initiating assembly passes, listing programs, and clearing table memory. Additionally, it offers a TYC (Type Control) mode, a debugging utility that allows programmers to inspect, search, and modify memory register contents in octal, or execute specific instructions.

Originally intended for remote programming via a Data-Phone (e.g., from California to a PDP-1 in Maynard), TC-FRAP proved highly beneficial for debugging large symbolic programs by enabling corrections to be made symbolically, maintaining clarity over time, rather than relying on abstract octal values.