How does one serial port send a break to another serial port? Is it some kind of special character?

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A serial break is not a character. It is a signal that can be sent using the TX line of the device sending the break.

When a serial port is idle and no data is being sent the TX line is in a logical 1 state. While data is being send the TX line rapidly transitions between logical 0 and logical 1. Each frame of data takes a certain period of time to send, depending on the bit rate of the connection. This is called the "frame time" or "word time".

A break occurs when the TX line is held to a logical 0 for longer than one frame time.

There are short breaks and long breaks. In general a short break is one that lasts longer than one frame time, but less than two frame times. A long break can last two or more frame times. Most serial devices that support breaks use a short break.

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[Originally Published On: 06/29/2002 04:21 PM]