Introduce

# RS-232 是最經典的序列通訊介面之一
RS-232 is one of the most classic serial communication interfaces.

# 用於電腦、工控設備、網路設備等設備間的點對點資料傳輸
Used for point-to-point data transmission between computers, industrial control equipment, and networking devices.

# 針腳定位如上圖所示
The pin positions are shown in the diagram above.

Situation

# 公頭無法跟公頭接
A male-to-male connection cannot be made directly.

# 需要母母的轉接頭，接上後卻不通
A female-to-female adapter is required; 
However, communication still fails after using the adapter.

Solution

# 母母的轉接頭因為沒有交叉，或是亂交叉導致兩邊公頭TX RX並沒有對到
The female-to-female adapter does not provide the required crossover, or introduces an incorrect crossover.
Causing the TX and RX lines on both ends to be mismatched.

# 電表使用電阻峰鳴模式來量測PIN腳如何交叉
Use the multimeter’s continuity mode to determine how the pins are crossed.

# 一邊接母A另外一邊接母B
Connect one probe to the pins on female connector A and probe the pins on female connector B.

# 當響鈴代表導通，可觀察出腳位對應關係
If the meter beeps, the pins are connected, allowing you to identify the pin-to-pin mapping.

Check

# 確認DTE與DCE的TX RX是否正確連接
Verify that the TX and RX lines between the DTE and DCE devices are correctly connected.