On Tuesday, March 17, 2020 at 1:21:05 PM UTC-4, Martin Eberhard wrote:
> I found the source listing for this boot loader on page 9 of the OS/8 System Reference Manual (DEC-S8-OSRMA-A-D). The comments in this code call this mystery 31 code "CODE BEFORE DATA WORD." This Mark Track code 31 seems to be undocumented in any of the tables of Mark Track codes I can find. What the heck is it?
The TC01 manual lists 8 mark track codes that have a compliment obverse, and 31 is one of the codes listed.
I looked through the DECtape formatter source and the hardware reference manuals for many DECtape controllers and didn't find any that use the Mark Track code 31.
Charles Lasner may be the only one who can answer your question.