Most probably this bus uses open-drain drivers with a pull-up resistor. Add a low-value resistor in series with the line to exacerbate any voltage drop. This way you can connect one of your scope's probe to each side of the resistor and then you will know when it is the master and when it is the the microphone that are pulling the line low. Possibly the microphone is pulling the line low after it sees the host pulling it low. When the host releases the line, the microphone keeps it low for the time it wishes, signaling a zero or a one. If that's true, you will see small "steps" in the signal when the host releases the line. Isaac Em 6/7/2012 17:41, Matt Bennett escreveu: > On Fri, July 6, 2012 3:15 pm, John Hansen wrote: >> I have been trying to decipher a communications protocol for some time n= ow >> with only limited success. It is used for communicating data between a >> microphone and the body of a radio transceiver (Kenwood D710 for amateur >> radio). All communication occurs on a single wire; there are not separat= e >> data and clock lines. In terms of the operation of the radio, there >> really >> isn't any need for bi-directional communication... data only needs to fl= ow >> from the microphone to the radio. >> >> I created a webpage that has the oscilloscope screen shots for the data >> captured flowing between the microphone and the radio. I have found how >> the data is encoded, but what I haven't been able to decipher is the >> handshaking that seems to be occurring between the two. >> >> If you have the time and inclination to take a look at this, I would >> appreciate any suggestions that you might have. Someone told me that th= ey >> have seen this before, but they are either unwilling or unable to tell m= e >> where or what it's called. They also suggested that a PIC lacked the >> horsepower needed to communicate using this protocol, but based on what >> I'm >> seeing on the scope, this seems to me to be very unlikely. >> >> The web page with the details is at: www.johnhansen.org >> >> Thanks in advance for any ideas! > I have not seen this protocol before, but this sure seems like a good > application for the "logic" analyzer: This > has the combination of very deep memory and fast enough sampling so you > should be able to record and decode the protocol. I can loan you mine fo= r > a short time if you're in the area (near Austin, TX), but the logic is > relatively cheap- just buy one! > > (just a happy user of the logic) > > > > Matt Bennett > Just outside of Austin, TX > 30.51,-97.91 > > The views I express are my own, not that of my employer, a large > multinational corporation that you are familiar with. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .