Yes, NMEA 0183 messages are a bit cryptic but in cleartext. The settings for NMEA 0183 are 4800 baud, 8 bits, No parity, and 1 Stop bit. Or in geek speak 4800, 8, N, 1.
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Sailingdog Telstar 28
New England
You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.
—Cpt. Mal Reynolds, Serenity (edited)
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SD - I won't go so far as to ask if it uses CTS/RTS for flow control.. I assume it's a bit more modern than XON/XOFF I can geek too...
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s/v "Pelican" Passport 40 #076- Cruising - BLOG - http://www.svpelican.com "Don't dream your life, live your dream" - Bob Bitchin'
"I'll see it when I believe it" - Me
SD - I won't go so far as to ask if it uses CTS/RTS for flow control.. I assume it's a bit more modern than XON/XOFF I can geek too...
I am pretty sure NMEA 183 does not use CTS/RTS, since it has no lines for that - it only has 3 wires for the connection. CTS/RTS requires a separate wire. It might, in theory, use XON/XOFF, but my experience developing for NMEA devices is that they don't use flow control at all. Since NMEA communication is usually one way (i.e. one device talks, another listens), and there really isn't much data, flow control is pretty much unnecessary.
SD - I won't go so far as to ask if it uses CTS/RTS for flow control.. I assume it's a bit more modern than XON/XOFF I can geek too...
Damn... Brak beat me too it... CTS and RTS each require signal lines... which NMEA doesn't require. The three wires in the NMEA are a data-in, data-out and ground... and if you are connecting a listen-only device, like a DSC-capable VHF, you only need two wires. The Standard Horizon 471 handheld has two wires for the NMEA GPS data in connection.
My guess is that Brak is right... that NMEA 0183 doesn't support any flow control whatsoever. That may be one reason the standard is limited to two talker devices per connection.
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Sailingdog Telstar 28
New England
You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.
—Cpt. Mal Reynolds, Serenity (edited)
If you're new to the Sailnet Forums... please read this POST.
Still—DON'T READ THAT POST AGAIN.
Last edited by sailingdog : 08-22-2007 at 09:43 AM.
Well, strangely enough, using Maptech's troubleshooting tool I can see the raw data stream and Maptech is receiving it correctly - it's just not displaying it correctly. I have a ticket open with them to see if they can figure it out...
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s/v "Pelican" Passport 40 #076- Cruising - BLOG - http://www.svpelican.com "Don't dream your life, live your dream" - Bob Bitchin'
"I'll see it when I believe it" - Me
Does Maptech have a patch or revision to the software that may have fixed this??
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Sailingdog Telstar 28
New England
You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.
—Cpt. Mal Reynolds, Serenity (edited)
If you're new to the Sailnet Forums... please read this POST.
Nope... I'm running the latest greatest... Hopefully there will be a patch, a fix, or a stupid realization on my part sometime soon!
__________________
s/v "Pelican" Passport 40 #076- Cruising - BLOG - http://www.svpelican.com "Don't dream your life, live your dream" - Bob Bitchin'
"I'll see it when I believe it" - Me
My guess is that Brak is right... that NMEA 0183 doesn't support any flow control whatsoever. That may be one reason the standard is limited to two talker devices per connection.
Well, that's just a property of serial links - only two devices get to talk to each other (each over another wire). Serial links don't have packetized communication the way anything with the bus does (like ethernet or other shared medium types). Sorry, offtopic, but that's my bread and butter
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.
BTW, I am fully aware that serial links don't packetize data... since i work in the IT field and have done quite a bit with serial communications for long distance data links as well as having almost two decades on experience with network architecture and design.
Quote:
Originally Posted by brak
Well, that's just a property of serial links - only two devices get to talk to each other (each over another wire). Serial links don't have packetized communication the way anything with the bus does (like ethernet or other shared medium types). Sorry, offtopic, but that's my bread and butter
__________________
Sailingdog Telstar 28
New England
You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.
—Cpt. Mal Reynolds, Serenity (edited)
If you're new to the Sailnet Forums... please read this POST.
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.
Or in geek speak 4800, 8, N, 1.
sometime soon!
