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Cedar Rapids, Iowa | "Baud" is another way to say "bits per second".
In the world of serial data, the value of a bit of data is determined by the voltage on a wire relative to ground. In the case of RS-232 (what we use in Ag), the voltage can swing from +25v to -25v. The baud rate is the number of times per second that the voltage can change.
Long long ago, when serial first got going, they started at 300 bps (bits per second). Eventually they doubled that and got 600 bps. Technology advanced and they were able to double it again to 1200 bps. As the electronics innovation progressed, they kept doubling the speeds - 2400 bps, 4800 bps, 9600 bps, 19.200 bps, 38,400 bps. At this point, they tripled 19200 to get 57,600 bps. Double that and you get 115,200 bps.
Not all devices can communicate at every speed I listed above. When two devices communicate, they both need to be set at the same speed.
If you choose too slow of a speed, you won't be able to transfer as many bits down the wire as you need to. When this happens, the sending device has a transmit buffer that eventually fills up, and then you lose some of the data. Imagine a football stadium full of people and everyone has to exit through a single gate.
On the other hand, too fast of a speed can be an issue too. If the wire connecting the two devices is long, then the voltage changes between bits won't be clear. The voltages start to blur and the receiving device can't clearly see data any more. I have seen issues at 115,200 bps on 50' long cables, but by dropping the speed to 57,600 bps, everything works fine.
-Lance | |
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Baud rates?
