NMEA versus RS232

[MarkJohnson12345]

A while back I asked about interfacing NMEA from an echo sounder to computer. All worked just fine, with one exception.

The number '8' and number '0' where downloaded as'<' characters.

The nmea to rs 232 is just a two wire connection. Have I missed something, or are the two protocols not quite compatable. I have tried three computer types, a Windows 95 laptop, which seemed OK, but not sire now, an old Husky Hunter, and a Psion workabout. On the latter, it accepts '8's as they come, bit '0's are substituted by '8's.

I am coming to the conclusion that the problem might be in the Garmin Echo sounder.

Any help appreciated

Regards

 

[pappaecho]

If the RS232 connection is just 2 wires, which are transmit and receive you will have to enable software handshaking, or Xon/Xoff, and by default disable hardware handshake, CTS/RTS. You also may be having problems with Data word length, stop bits and even whether it is ASCII or extended ascii.. Best to talk to Garmin Tech support, and then set the computer to the correct data word length, stop bits etc

 

[qetoo]

Pin 2 on the computer RS232 serial connector is for Receive Data.
Pin 5 on the computer is the common wire.

I have posted my wiring diagram at:
http://carlten.tripod.com/Navigation/navigation.html

The computer RS232 connection must be set for the NMEA data format. I believe the NMEA 0183 standard is 4800 bits per second, 8 data bits, no parity, one stop bit, and Xon/Xoff.

 

[MarkJohnson12345]

Many thanks for the help.

I have written a programme to correct the errors, but will also follow up to Garmin.

Great web page Carl, really enjoyed reading it.

Regards