prv
Well-Known Member
I have to say that, having a degree in electronic engineering and having worked as a computer engineer in the past, plus being a radio amateur for the last thirty-odd years, I had never come across a single serial port that was capable of operating at different speeds on send and receive until I looked at some modern chart plotters!
I know, but from the user's point of view, these aren't single ports with bidirectional capability, they're a collection of independent inputs and outputs. You have "x NMEA input pairs and y NMEA output pairs", not "max(x, y) two-way ports". Looked at like this, the speed restriction seems artificial. They could (and probably should) have used two hardware serial devices so that they could run them at different speeds.
The plotter supports AIS, so it's highly likely that the input will need to be set to 38400. Everything else that NMEA is used for runs at 4800, so the output will need to be set to that. With a single serial chip, you're effectively reduced to using only one of these in any given installation. Daft design to save a few pence.
Pete