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AN197

更新时间： 2022-04-23 23:00:11

品牌	Logo	应用领域
芯科 - SILICON		通信
页数	文件大小	规格书
14页	234K
描述
SERIAL COMMUNICATIONS GUIDE FOR THE CP210X

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AN197 数据手册

AN197

8. Application Design Notes

The functions used in section 3., section 4., and section 5. are Windows COMM API functions. The examples

provided are just samples of the recommended way of dealing with serial communication. For more specific

information on these functions, see the MSDN website at: http://msdn.microsoft.com/library/default.asp.

It should also be noted that the SetCommState() function does not save the settings between opening and closing

the COM port. As stated before, it is good practice to get the current settings after the COM port is opened, and

then restore them before it is closed.

All of the functions here will return an error code. It is a good idea to nest these functions in order to catch errors if

they occur by using the GetLastError() function. This will also solve any surprise removal problems by allowing the

discovery of an invalid handle to be found and dealt with. The example application (CP210xSerialTest) has several

cases that will detect surprise removal. In this example, there are checks on every function to make sure that the

return code is true. If it is not, then it will display where the error occurred in the output window. As long as correct

and supported settings are passed to the functions they should execute normally. Most failures can occur from

having an INVALID_HANDLE_VALUE, however, the handles must be set to this value after a surprise removal

occurs.

Because regular COM ports will always be visible, then data can always be written to them successfully, even if

there is no way to read it. However, because the CP210x is a virtual COM port, if the device is removed, then the

handle that it uses becomes invalid when trying to write to it. If for some reason the CP210x device is unplugged

the write will fail and ERROR_OPERATION_ABORTED will be returned by GetLastError(). When this happens, the

handle needs to be closed and then set to INVALID_HANDLE_VALUE. Alternatively, a regular COM port can

always be read from, but if there is no data then it will time out. When using the CP210x as the virtual COM port

and it is removed before a read occurs, then the read will fail and ERROR_ACCESS_DENIED will be returned by

GetLastError(). Again when this happens, the handle needs to be closed and then set to

INVALID_HANDLE_VALUE.

9. References

MSDN - use this to search for specific Windows API functions

http://msdn.microsoft.com/

Serial Communication Reference

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnfiles/html/msdn_serial.asp

Communication Resource Reference

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/devio/base/communications_resources.asp

Rev. 0.6

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