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How to test the COM port of mainboard

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1. Short jumper to test serial 2,3 pins (D-type interface for a wider side from the left or from on the 2,3 feet, at the bottom of the pin has small logo);

2, open the computer, enter the operating system, click Start - all procedures - Annex(Win98/Win2000 /WinME/WinXP )create a super terminal, in the "connection" window of the pop up,Enter any name after the point "ok"

3, in the "connect to" window, select the port (which is to test the port), the point "determine

4, in the "COM1 properties" window, the point "restore to the default value" - "OK.""

5, enter any character on the keyboard to see if the super terminal can display the character of the input,

If no return, it is to test the serial port is bad.



Test Description: by default, the super terminal input characters on the screen is not echo, shown here should be to receive port test of character, such as removing the jumper, you can find will not display the input character.

Therefore, using this method, as long as the screen has a back marked character,

Which means that the serial transceiver function normal! If you do not have the problem of serial port.


Tool test 9 pin serial line is good or bad

9 pin 25 pin definition of voltage (DC)

1 feet: carrier detect -0.07~-0.15V DCD

2 feet: accept data -0.07~-0.15V RXD

3 feet: send data -10V~-12V TXD

4 feet: data terminal ready -10V~-12V DTR

5 feet: system ground 0V SG (ground)

6 feet: data ready -0.07~-0.15V DSR

7 foot: request to send -10V~-12V RTS

8 feet: clear send -0.07~-0.15V CTS

9 feet: RI -0.07~-0.15V ring indicator

Test method using a million:

The A.3.4.7 pin voltage value should be basically the same, generally the actual measured voltage is about -11.10V, or serial fault.

B. pin voltage should be exactly the same. In general, the actual measured tramp voltage is about -0.14V, slightly has the difference, can be judged for the serial fault.

C.5 pin because the ground should be 0V, otherwise this pin is not connected to the serial port work will not be normal.


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