Modify existing VB6 program to be able to communicate with more items URGENT

Hi, we have an existing VB6 program which we use to control a multitude of gas analysis instruments. We have developed a new range of analysis instruments which have slightly different communication protocol (based on German automotive AK protocol). The existing software must be able to communicate correctly with both legacy instruments (as it currently does), and the new equipment. Also it must be able to address a larger number of PLCs than it currently can. It is currently limited to 2-bit addresses but it requires 3-bit. I have attached a more detailed spec.