Sure, but it is not a bus. It is a standard serial connection. One wire carries data, one is common "ground". Two wires carry data from A to B and from B to A, each. As with any serial connection, you can "tap" off of it to devices that are pure listeners. Since there is nothing specific on the wire other than simple time series of bits (essentially voltage on - voltage off, read off the wire at given times), listeners can listen all they want, they just can't say anything. In fact, I am guessing that a limitation of 4 listeners is simply to reduce power requirements (the more listeners, the higher the power would have to be and standard UART chips or whatever they use now in these devices) probably have defined power output that can't be easily changed.
I don't doubt your credentials, and this is not meant in any negative way
Quote:
Originally Posted by sailingdog
Brak-
I think you're a bit confused. The NMEA 0183 specification, IIRC, allows two talker devices on a single NMEA 0183 bus, but up to four listener devices.
|