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Old 04-07-2009, 01:12 PM   #786 (permalink)
esoneson
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Quote Paul: "So, when I want to send characters by the serial port to SOMETHING, what is the something? What are the settings of that something, like with the even, odd, and no parity, etc... I have no something in the car right now."


RS232 is a very well defined standard that has been in use for decades (literally). What you should do is to pick a set of commonly used parameters that most RS232 based programs use or can easily be configured to (i.e. Hyper Terminal in Windows, Tera Term program in Windows).

The Rx and Tx pins in the atmegaXX need to have their signal modified to fit the stringent requirements of the RS232 standard, that is why the MAX232 chip is there. It might work without it for some RS232 interfaces but we want it to be reliable for all RS232 interfaces. The MAX232 puts the signal within the acceptable range for RS232.

OK, now for the suggested settings:
Data Rate (baud) 19,200 bits per second. Most programs can go up to 56K. I see no need here to go faster and 19.2K can be handled by most all applications. If you think of any that may have trouble at 19.2 then we can always set the default speed (data rate, baud) to 9600 with no serious consequences.
Parity - none
Stop Bits - 1
Flow Control - no

You will be able to connect most any RS232 device to this interface and be very happy with the results. I don't think that we should offer a configurable RS232 interface within the controller at this time, but it is not that big of a deal if it becomes necessary.

Whatever we set the RS232 parameters to in the controller, we have to publish those settings so that the user can set the RS232 parameters at his end to match.

Capiche?

Eric
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