It may have even been machine code or some assembly language -
"load c, add hf, move b" etc,
I wrote the code for an engine management system with this stuff - microchip pic 16f87, it ran the ignition and fuelling, quite well actually. I would love to get back into it but can't seem to find the time.
While you were writing the above I was looking it up and yes, Voyager runs on Assembly Language (to those of you who might not know, Assembly Language is about as low level coding as you can get), as well as higher level languages like Fortran and COBOL. Fortran I can understand as it is a scientific language but as for COBOL, I was surprised. I think of it more as a business related language because of its name (COmmon Business-Oriented Language) and the type of programs I used it for. I actually liked COBOL, it was quite disciplined if used properly.
While looking, I came across a piece that said NASA was looking for coders who could work in 60 year old languages to work on Voyager! Maybe you and I, Minimutly should apply. Can I work from home?