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The so-called chip selection signal refers to the main board of the traditional north-south bridge architecture,Address lineSeparate from data lineBIOS chipThe signal of pin 22 in the.It is sent by the CPU and arrived by the North Bridge and the South Bridge.Whether it is available or not can preliminarily judge whether the North South Bridge and the CPU are working, and whether the BIOS data is damaged.
If you want to see this signal, you must remove the BIOS chip and observe it with an oscilloscope at pin 22 at the moment of power on.
However, it is difficult to describe it. In short, after you have installed the CPU, at the moment of startup, you can see that 22 pins on the oscilloscope show that when the voltage rises, it is about 1V (the starting point of the voltage is 0V, that is, the horizontal line when there is no voltage is 0V), and there is an obvious small light spot that flashes. This light spot is the chip selection signal.Generally, this process is very short. It takes less than half a second from 0V to 3V or 5V. The flash of light is even shorter.Therefore, it is necessary to repeatedly trigger the power supply with the trigger switch to see the flashing signal.
Selection judgment
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Normal motherboardFilm selection, (Only the North South Bridge architecture is available, that is, the old motherboard, not the HUB-LINK architecture above 810). How to judge? Let me teach you a method. In fact, in actual maintenance, few people directly test it. Instead, they test any AD line on the PCI slot at the moment of starting up. If there is an instant parallel bar wave, it means that there is already a piece selection, or in the process of triggering,If there is a transient double wave jump of BIOS A line, D line, or CS signal, it also proves that a chip has been selected.You don't have to take it downBIOS chipEspecially the BIOS welded on the board.If the waveform is always a single DC voltage at this moment, the chip selection signal has not arrived, which may be caused by the CPU not working or the internal problem of the north-south bridge.
Chip selection can be understood as chip selection. When many chips are hung on the same bus, a signal is needed to distinguish which chip processes the data and address on the bus. At this time, a chip select signal CS (chip select) is needed, which is generally divided intoaddress spaceIt is generated by logic circuit.In digital circuit design, the open circuit input pin is generally high level, so chip selection signal is mostly low level.
