| ??? 05/20/10 09:30 Read: times Msg Score: +1 +1 Informative |
#176058 - Asymmetry Responding to: ???'s previous message |
I was bitten by asymmetry recently. Most uarts oversample at 16x the bit rate and use the middle 3 bits as the bit value. This means that you can tolerate a mismatch of 0.4 bit times over 10 bits, which is 2% each when split between TX and RX. Not all uarts work like that, and one device had a low power mode that meant it only sampled about 3x the bit rate. Even though my rates were matched to better than 0.2%, I was getting bad comms because the channel was introducing asymmetry (nobbled mark:space ratio). Switching off the low power mode fixed my particular problem. |
| Topic | Author | Date |
| Baud RateTolerance? | 01/01/70 00:00 | |
| acceptable baud-rate error | 01/01/70 00:00 | |
| 100% ?? | 01/01/70 00:00 | |
| 2.5% | 01/01/70 00:00 | |
| whoa!! | 01/01/70 00:00 | |
| I prefer < 0.5% | 01/01/70 00:00 | |
| the method | 01/01/70 00:00 | |
| skew/asymmetry | 01/01/70 00:00 | |
| Asymmetry | 01/01/70 00:00 | |
| ZERO | 01/01/70 00:00 | |
| So do I... | 01/01/70 00:00 | |
| Not always possible to select crystal just for UART | 01/01/70 00:00 | |
| In reference to the above: | 01/01/70 00:00 | |
| Thank you all. | 01/01/70 00:00 | |
| Try a test with a PC and Sqr Sig Gen | 01/01/70 00:00 | |
| likely a wromg approach | 01/01/70 00:00 | |
| Maxim AN-2141 | 01/01/70 00:00 | |
link and comment | 01/01/70 00:00 |