Timing contraints driver switch from controller to responder

[ericthegeek]

Originally Posted by mkoelman

I do not think the responder can detect the bus not being driven anylonger, as the biasing circuitry will pull the bus high if undriven (true?).

In a properly functioning RDM system you never need to detect whether the bus is being driven or not. Bus access is entirely determined by timing.

The biasing circuitry will pull the bus high when it is un-driven, but this can take a while due to capacitance on the wire. That's why RDM devices are required to drive the bus high before they disable their line drivers. This way the bias circuit only has to maintain the bus state, not change it.

Originally Posted by mkoelman

Does this mean that the responder will always have to wait the full 88usec
before it can initiate a break?

Response timing is defined by E1.20-2010 Table 3-4 "Responder Packet Spacing Times". A responder must wait a full 176us before it can initiate a break.