What was the communication protocol used on board the Apollo moon lander?
Dig in here: ftp://ssh.esac.esa.int/pub/ekuulker/Apollo15/The-Apollo-Guidance-Computer-Architecture-and-Operation.pdf
And here: https://arstechnica.com/science/2020/01/a-deep-dive-into-the-apollo-guidance-computer-and-the-hack-that-saved-apollo-14/3/
tl; dr: a bespoke binary stream format for telemetry uplink and downlink.