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Teach you how to test the main board serial port failure

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Software operation method

1. The 2 or 3 pins of the serial port should be tested with the short jumper connection (the second or third pins of the wide side of the d-type interface are from the left or from the top, and there is a small mark at the bottom of the pin);

2. Open the computer, enter the operating system, and click start - all programs - attachments - communications - super terminal (Win98/Win2000 /WinME/WinXP are the same). Set up a super

Level terminal. In the pop-up "connection description" window, enter any name and then click "ok".

3. In the pop-up "connect to" window, select the port used when connecting (i.e. the port to be tested) and click "ok"

4. In the pop-up "COM1 attribute" window, click "restore to the default value" - "ok"

5. Input any characters on the keyboard to check whether the input characters can be displayed at the super terminal. If there is no echo, the tested serial port will be broken.

Test description: by default, the characters entered in the super terminal will not be echoed on the screen. What should be shown here should be the characters received by the port to be tested, such as removing the jumper

To find that the input characters are no longer displayed.

Therefore, in this way, as long as you see the screen has echo characters, that means that the serial port transceiver function is normal! If not, of course, there is a serial port problem.

Tool to test the quality of 9 needle serial line

9 pin 25 pin pin defining voltage (dc)

Foot: carrier detection DCD -0.07 -0.15V

Foot 2: accept data rxd-0.07 ~-0.15V

Foot 3: issue data txd-10v ~ -12v

Foot 4: the data terminal is ready for dtr-10v ~ -12v

5 pin: system ground wire SG 0V(ground)

6 feet: data preparation dsr-0.07 ~-0.15V

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

Foot 8: clear sending CTS -0.07~-0.15V

Feet: ring indicating RI -0.07~-0.15V

Test method using multimeter:

Judgment criteria:

A.3.4.7 the voltage value of the foot should be basically the same. Generally, the actual measured voltage is about -11.10v, otherwise, the serial port will fail.

B. the foot voltage value should be exactly the same. Generally, the actual measured voltage is about -0.14v, and any slight difference can be judged as a serial port fault.

C.5. Because the grounding shall be 0V, otherwise the needle shall not be grounded properly and the serial port shall not work normally.

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