| ??? 03/27/09 10:02 Read: times |
#163896 - You were clear Responding to: ???'s previous message |
Andy Neil said:
Ap Charles said:
http://en.wikipedia.org/wiki/Fall_back_and_forward
Fall back is a feature of a modem protocol in data communication whereby two communicating modems which experience data corruption (due to line noise, for example) can renegotiate with each other to use a lower-speed connection. Fall forward is a corresponding feature whereby two modems which have "fallen back" to a lower speed can later return to the higher speed if the connection improves. Ah; I'm just interested in the local speed between the microcontroller (DTE) and the modem (DCE) - not the "line" speed. Sorry if I didn't make that clear. It says:- "They would start at high speeds and progressively get slower and slower until they heard an answer. " Andy Neil said:
Steve M. Taylor said:
Well you might short circuit the process by guessing its unlikely to be <1200 baud or > 115K ? Yes - that's where I was heading with talking about the microcontroller's "preferred" speed... The naive approach would be just to start at 300 and work up to the microcontroller's maximum - say 115k2; but, if the modem autobauds, that leaves you stuck unnecessarily at 300. (conversely, if you start at 115k2, you might not want to get stuck there, either) So I guess I need a list that starts with the "preferred" rate(s), then other "most likely" rates, then the rest... As well as not knowing the modem's baud rate in advance, I also don't know if it will have command-echo enabled - so I'll also have to cope with the possibility of receiving garbage echo when the rate is wrong... Even if its between uC and a Modem you do it other way from slower to higher baud this can take more time . If the modem is responding with some error code (for not recoganised baud) maybe you could check at what frequency that error code is being sent with your uC .If that keep comming for more than a couple of time, Just a thought. -Ap |
| Topic | Author | Date |
| Autobaud - the other end... | 01/01/70 00:00 | |
| Doh | 01/01/70 00:00 | |
| Eh? | 01/01/70 00:00 | |
| Homing in | 01/01/70 00:00 | |
| Considerations | 01/01/70 00:00 | |
| How does it respond to AT? | 01/01/70 00:00 | |
| The proper response to "AT" is "OK" | 01/01/70 00:00 | |
| no absolutely perfect solution | 01/01/70 00:00 | |
| Character time | 01/01/70 00:00 | |
| Go for KISS | 01/01/70 00:00 | |
| only be needed once after a modem change. | 01/01/70 00:00 | |
| Some ARM7's have Autobaud detect | 01/01/70 00:00 | |
| No - the *other* end! | 01/01/70 00:00 | |
| Fall back and forward | 01/01/70 00:00 | |
| Only interested in local DTE-DCE speed | 01/01/70 00:00 | |
| You were clear | 01/01/70 00:00 | |
| Start slow, or start fast...? | 01/01/70 00:00 | |
| Unnecessarily high? | 01/01/70 00:00 | |
| High baudrate = bursty | 01/01/70 00:00 | |
| Throughtput | 01/01/70 00:00 | |
| Keep Up? | 01/01/70 00:00 | |
Keeping up always hard at high baudrates | 01/01/70 00:00 | |
| KISS? | 01/01/70 00:00 | |
| A Cunning Plan... | 01/01/70 00:00 | |
| Timing | 01/01/70 00:00 |