vb可以控制串口发出一个连续的4s长度的低电平信号吗？

chaoshuai

如题   想利用串口发送一个持续的低电平，用来唤醒睡眠中的单片机

fnems

空闲状态的TxD是逻辑1，串口使用负逻辑，所以空闲状态的串口是低电平。

这样能满足LZ要求吗？

chaoshuai

谢谢.楼上啊。.
我没有说明白.

就是让TxD发送逻辑0,经过max232转换之后 输出一个 TTL 的低电平.

zxq6

用CTS（RTS）把

chaoshuai

thank you ..
楼上说说看， 具体怎么实现啊?  查了半天没查到.

fnems

在Windows环境下，帖一个API：

The EscapeCommFunction function directs a specified communications device to perform an extended function.

BOOL EscapeCommFunction(

    HANDLE hFile,        // handle to communications device
    DWORD dwFunc         // extended function to perform
   );       


Parameters

hFile

Identifies the communications device. The CreateFile function returns this handle.

dwFunc

Specifies the code of the extended function to perform. This parameter can be one of the following values:

Value        Meaning
CLRDTR        Clears the DTR (data-terminal-ready) signal.
CLRRTS        Clears the RTS (request-to-send) signal.
SETDTR        Sends the DTR (data-terminal-ready) signal.
SETRTS        Sends the RTS (request-to-send) signal.
SETXOFF        Causes transmission to act as if an XOFF character has been received.
SETXON        Causes transmission to act as if an XON character has been received.
SETBREAK        Suspends character transmission and places the transmission line in a break state until the ClearCommBreak function is called (or EscapeCommFunction is called with the CLRBREAK extended function code). The SETBREAK extended function code is identical to the SetCommBreak function. Note that this extended function does not flush data that has not been transmitted.
CLRBREAK        Restores character transmission and places the transmission line in a nonbreak state. The CLRBREAK extended function code is identical to the ClearCommBreak function.


Return Values

If the function succeeds, the return value is nonzero.
If the function fails, the return value is zero. To get extended error information, call GetLastError.

See Also

ClearCommBreak, CreateFile, SetCommBreak

fnems

vb有一个API字典工具，找 EscapeCommFunction 这个函数，加入它的引用，就可以用了。

chaoshuai

顶一个， 谢谢楼上各位。