I'm still looking for information about the system 21 bus. I've found out that this was also known as D2B or Domestic Digital Bus, through the service manual of a Philips multimeter. Unfortunately it seems like there are two busses with the same name, there's also an automotive system called D2B which uses optical cables. It's briefly mentioned in the sci.electronics faq about I2C: "Offspring like D2B and ACCESS bus" and other places, but I seem to only find links to the automotive bus... Can anyone help me out or give me some hints where to look for this? Names of companies or equipment that used this would also be helpfull.
greetings, Michiel