Timeline for In one-way asynchronous serial communication, how does the receiver sync up its bytes?
Current License: CC BY-SA 3.0
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| Apr 30, 2018 at 15:58 | comment | added | Adam Davis | @supercat Yes, and we could go on. It is an interesting discussion because I'm sure there are cases where one would make more sense than the other and vice versa depending on the requirements and specific environment. I personally wouldn't use either unless required - they're both really scraping the bottom of the barrel. I used a low sample rate to illustrate the answer and make it simpler, but suggest a higher sample rate in general. | |
| Apr 30, 2018 at 15:52 | comment | added | supercat | With 3x, you get one sample that's at least 1/3 of a bit time away from the edge. With 4x, you get two that are 1/4 away. If both samples match on every bit, that would suggest that are probably good, but if they don't match you may not know which one is "right". BTW, another approach which I'm surprised I don't see more often implemented is to use 2x oversampling but reset the timer when the start bit is received. | |
| Apr 30, 2018 at 15:37 | comment | added | Adam Davis | @supercat Probably a good discussion for a follow up question. There are merits to both, however with 3 you can really only trust one sample, the other two could be very close to the transition and without additional effort you don't know which of the other two you can trust. With 4 you get two samples that are known to both be at least 1/4 bit time away from the transition. This being a simple example I didn't go further, but certainly depending on the actual noise experienced one or the other might perform better. | |
| Apr 30, 2018 at 15:25 | comment | added | supercat | Using an odd oversampling multiple works slightly better than an even one. Using 3x oversampling, for example, allows for a full +/- 1/3 of a bit time worth of slop, while using 4x only allows one to allow for either -1/2 +1/4 or -1/4 +1/2. | |
| Apr 30, 2018 at 13:48 | history | answered | Adam Davis | CC BY-SA 3.0 |