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Go Back   SailNet Community > On Board > Gear & Maintenance > Raymarine Output Problems
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Thread: Raymarine Output Problems Reply to Thread
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Topic Review (Newest First)
09-11-2007 07:44 PM
sailingdog Don't hold your breath...
Quote:
Originally Posted by labatt View Post
Just got an e-mail from Maptech... the problem is indeed a bug and will be fixed in the next release (who knows when that will be).
09-11-2007 07:26 PM
labatt Just got an e-mail from Maptech... the problem is indeed a bug and will be fixed in the next release (who knows when that will be).
08-27-2007 12:11 PM
labatt
Quote:
Originally Posted by brak View Post
Indeed, one transmitter - one wire. But you can connect more than one listener to that same wire, as long as there is enough power in there to drive them. Probably not the optimal way to do things, though.

Now I do wonder how they deal with that in Seatalk. It runs an actual bus over 2 wires (with multiple talkers and all).
Collision control - something that doesn't exist within the NMEA 0183 standards but does exist on the 2000 standards. With regards to putting multiple listeners on the same wire, I'd probably hesitate to do that. Unless you are really good at crimping and creating taps, a single additional listener could cause a large voltage drop and then NONE of your devices would work. I'd lean heavily towards an active multiplexer. I hate tracing electrical gremlins.
08-26-2007 11:10 PM
brak Found it - http://www.thomasknauf.de/rap/seatalk1.htm, wow - thats a sweet protocol.
08-26-2007 11:07 PM
brak Indeed, one transmitter - one wire. But you can connect more than one listener to that same wire, as long as there is enough power in there to drive them. Probably not the optimal way to do things, though.

Now I do wonder how they deal with that in Seatalk. It runs an actual bus over 2 wires (with multiple talkers and all).

Quote:
Originally Posted by labatt View Post
Correct me if I'm wrong, but while the standard allows for multiple talkers it can only be done via a multiplexer... the multiplexer will act as a hub, aggregate the inbound datastreams and then output them to as many listeners as the multiplexer can support. Now I have to go do some research to verify this... I can't see how a serial connection could have more than one device outputting at one time though... Since it's really just a series of electrical impulses and there is no collision control on serial, it would just seem like a mess to any listening devices, wouldn't it?
08-26-2007 10:49 PM
labatt Correct me if I'm wrong, but while the standard allows for multiple talkers it can only be done via a multiplexer... the multiplexer will act as a hub, aggregate the inbound datastreams and then output them to as many listeners as the multiplexer can support. Now I have to go do some research to verify this... I can't see how a serial connection could have more than one device outputting at one time though... Since it's really just a series of electrical impulses and there is no collision control on serial, it would just seem like a mess to any listening devices, wouldn't it?
08-26-2007 09:23 PM
brak 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 View Post
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.
08-26-2007 09:12 PM
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.

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 View Post
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
08-26-2007 08:06 PM
brak
Quote:
Originally Posted by sailingdog View Post

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
08-26-2007 08:56 AM
labatt Nope... I'm running the latest greatest... Hopefully there will be a patch, a fix, or a stupid realization on my part sometime soon!
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