The reset key of desktop computer is generally near the start key on the chassis, and the reset key of notebook computer is at the top of the keyboard. At the same time, press CTRL+ALT+DEL on the computer keyboard to reset, which belongs to soft reset, also called hot start.
principle of operation
The reset key is started after clearing the current CPU and running data. It does not involve power failure.
All reset signals on the motherboard are generated by the chipset, mainly by the South Bridge (with reset system controller inside) or the reset generator (74H series chips), which means that all devices and modules on the motherboard need to be reset by the South Bridge. If South Bridge wants to generate reset signals or reset other devices and modules, it must first reset itself or have its own reset source. The reset source of South Bridge is the gray line of ATX power supply, or
First of all, after the power supply is started, ATX power supply sends out power supply normal signal PWRER OK, that is, ATX PWRGD, which is shaped by inverter HCT 14 and then outputs CLROFF signal, which enters South Bridge 8237 1 to clear its internal register, and is also input to NAND gate HC 132. When the voltage reaches the rated value and is stable, the voltage control chip sends out a VRMPWRGD signal, which is also input to VHC 132. These two signals enter VHC 132X logic operation, and the output signals are shaped by HCT 14, and then output to the south bridge through the PIN 10 of HCT 14. Due to the gray color of ATX power supply,
This delay process is equivalent to yellow line and red line, and the delay time is 100 ~ 500 ms, which means that the gray line will have a low-level to high-level change process when the ATX power supply works, that is, the level signal will change from 0 to 1. First, reset the South Bridge and the North Bridge. When the South Bridge is reset, the reset system controller inside the South Bridge will send out RSTDRV signal, which will decompose the gray line 5V signal into ISARST, and ideRSTDRV will reset ISA slot and IDE interface and send out PCIRST signal.
South Bridge sends out other reset signals (commonly used in notebook circuits). On some motherboards, the PG signal of CPU is directly provided by the PG signal of power manager, while others are indirectly provided by the gray line of ATX power supply. Usually, the reset circuit on the motherboard is controlled by a reset switch. One end of the reset switch is low and the other end is high. The low level is usually grounded, and the high level is indirectly powered by the red line and the gray line. One end of the reset key, usually 3.3V, will also directly or indirectly act on the south bridge.
The high-level end of the switch will generate a low-level signal, which directly or indirectly acts on the reset system controller in the South Bridge, so that after the South Bridge is forcibly reset, the South Bridge will also forcibly reset other devices and modules, thus realizing a forced reset process, which is commonly called cold start. When pressing CTRL+ALT+DEL key for hot start, 37 1 will send out BIOSRST signal, and the signal will be reset at PIN9 input of U 18.