M-1123 Aug61

This permanent memorandum, M-1123, dated August 29, 1961, outlines the "Read Binary Test," a utility program designed for PDP-1 Maintenance Personnel.

Its primary purpose is to thoroughly test the performance of the PDP Reader. The program operates by continuously reading a closed loop of magnetic tape specifically prepared with an alternating pattern of ones and zeroes. After each "rpb" (read paper tape binary) command, the reader transfers data through its buffer to the I/O unit and then to the accumulator, where all 18 bits are immediately checked against the expected pattern stored in core memory.

Maintenance personnel can adjust various parameters during the test, including the timing between read commands (using test word switches 0-18) and the tape's reading speed (switches 0-17). Crucially, the test allows for the variation of +10 volt margins on the reader, Input Mixer, and In-Out logic, enabling the identification and logging of specific voltage thresholds and bits that cause read errors. Upon detecting an error, the computer halts, displaying the error in the accumulator and the faulty word in the I/O.

The memorandum includes the program listing for the Read Binary Test, as well as instructions and code for generating the required alternating ones and zeroes test tape.