Demon, Thats the beauty of an open collector buses is there can be an unlimited number of devices connected. Any device can respond to a command and any device can be the master. Over current collisions are avoided by there only being 1 set of pullup resistors that source the current to the bus. If 2 devices try to talk at the same time there is no excessive current drawn. Therefore there needs to be a standard protocol that is used in the communications scheme. I have had more than 32 devices on a single bus in the past without any problem. The resistors are sized by the time constant to clear the ground condition produced by the device that is talking on the bus. Therefore to talk at higher speeds the pullups need to be smaller in size to enable more source current to the bus to clear the ground condition.
Dave Purola,
N8NTA
Bookmarks