A question about baud rates...

fogled@mizzou

When I started with AMX stuff, almost everything I ran into was set to 9600 baud. But after my experiences with BiAmps and Polycoms, I'm thinking that I want to crank up baud rates as high as I can.

How do others approach baud rate settings?

vincen

Well you just add in your program in the online of a DATA_EVENT for each serial device the command as is:

SEND_COMMAND DATA.DEVICE,'SET BAUD 9600,N,8,1 485 DISABLE'

You just adjust accordingly to device controled speed, parity, length and stop bit and everything is same in program

Hope it helps

GSLogic

fogled@mizzou wrote:

When I started with AMX stuff, almost everything I ran into was set to 9600 baud. But after my experiences with BiAmps and Polycoms, I'm thinking that I want to crank up baud rates as high as I can.
How do others approach baud rate settings?

You can only set the baud rate as high as the device will allow. If there are different setting for the device's baud rate, keep in mind faster is not always better. Some device need time to process commands, so if you increase the baud rate you'll have to use a que to hold the commands until the device has processed them before receiving the next command.

fogled@mizzou

Most devices, technically, support up to 115200 baud. I've also discovered that many devices have no flow control and no buffering, so I've got to implement a command/response flow control anyway. Over the last couple of weeks, I've ended up testing a wide range of baud rates (from 2400 to 115200) on several different devices, and I've found that slower baud rates do NOT equate to fewer dropped commands, nor do higher baud rates cause more problems. The only real "fix" for serial devices dropping commands has been to implement a command/response flow control.

Longer serial cables force lower baud rates, of course. I've left all my projectors at 9600 baud since they are usually a fair distance from the controller. Projectors just don't get a barrage of commands that could be dropped, either. But for devices in the same rack as the controller, cable length isn't an issue, and sometimes I have to send several commands in a row to the device. So I've been upping the baud to 115200 (or at least 57600) on these devices, and it seems like it makes the whole system just a bit "snappier".

Does anyone know whether slower baud rates actually slow down the controller? It seems like the faster I can get commands in and out of the controller, the more time the controller has to chew away on the program and be more "responsive". Then again, maybe each serial port is buffered from the CPU itself, and the actual data sending is handled by a separate serial controller. Any comments on that?

jweather

PCs, and presumably AMX controllers, offload the serial encoding/decoding process to a chip called a UART (http://en.wikipedia.org/wiki/UART). The amount of buffering done depends on the chip, but I doubt that changing baud rates affects your CPU usage very much at all.

Jeremy

ericmedley

Another consideration...

I tend to leave all serial devices controlled at their factory or default baud settings. I find that it's a little more fool proof. If the device somehow gets zapped or someone comes along and resets it, it comes up in factory settings. If you work with the factory settings, you tend not to get into trouble in that regard.

I typically don't find most device's serial communication to be so slow that it's unusable. Even home security systems which are painfully slow. (1200 baud) seem to do alright for most applications.

NMarkRoberts

Keep it safe

I can't see any reason to change the factory setting. I can think of reasons not to - like confusing the next guy to work on the system, or making it impossible to replace a faulty unit without looking at the code.

DHawthorne

I don't change baud rates anymore either, unless the default really is unacceptably slow. For most controlled devices, the amount of stuff going back and forth doesn't require a higher speed anyway. For me, it's just not worth the hassle when a box needs to be replaced or swapped out, going through with the techs how to change the baud rate, and what to change it to ... to say nothing of something happening that resets it to default. It's just simpler all around to leave it alone.

That said, if there is a lot of traffic, a slow baud rate just won't cut it. A media server, for example, like an Escient Fireball, would really populate a panel slowly at 9600. That you would want to bump up.

Most devices, I consider 57600 to be the practical upper limit. 115200 seems to generate errors, especially with longer wire runs.

Chip Moody

The only devices I currently change from factory defaults are NEC projectors. We had a run of projectors some time ago that were flaky at best at the default of 38.4. After some investigation, the consensus - from tech support folks, no less - was to set the projectors to 9600. Ever since then, that's been SOP. Not taking any chances that NEC cleaned up their projector com ports since then or not, y'know? Why not just be safe...

- Chip

fogled@mizzou

Thread Wrap-Up

OK, I think I get the gist:

1. Leave baud rates at factory defaults, unless you have a REALLY good reason not to.

2. If you do change it, your documentation had better be good. Really good.

Simple enough?

Thanks for the input everyone!