| ??? 03/27/09 09:13 Read: times |
#163892 - Fall back and forward Responding to: ???'s previous message |
Andy Neil said:
My basic approach would be to just send "AT" at various speeds until I get a proper "OK" response. This looks only the descent and proper approach. Andy Neil said:
But are there any cunning tricks that could speed the process? eg, I guess I should start at the microcontroller's "preferred" speed - in case the modem itself is autobauding! Any other thoughts? 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. A common feature modems was the concept of fallback, allowing them to talk to less-capable modems. During the call initiation the modem would play a series of signals into the line and wait for the remote modem to "answer" them. They would start at high speeds and progressively get slower and slower until they heard an answer. Thus, two USR modems would be able to connect at 9600 bit/s, but, when a user with a 2400-bit/s modem called in, the USR would "fall back" to the common 2400-bit/s speed. This would also happen if a V.32 modem and a HST modem were connected. Because they used a different standard at 9600 bit/s, they would fall back to their highest commonly supported standard at 2400 bit/s. The same applies to V.32bis and 14400 bit/s HST modem, which would still be able to communicate with each other at only 2400 bit/s. A modem that can fall back in order to communicate with an older, slower modem is an example of backward compatibility. A modem that can fall back in order to communicate when the line becomes noisy is an example of graceful degradation. Fall back is also a military term and command meaning to retreat and temporarily cease combat. It is also a nickname for when Daylight Saving Time ends each year, referring to how clocks are set back one hour in the fall, hence 'fall back'. After Fall Back, the sun sets one hour earlier. In military slang, it is a term used on the battlefield to retreat; i.e., falling back to another position. -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 |