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Hello everyone, today we continue to analyze the timing of the Wistron 15221 motherboard

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In the last class, we talked about how the standby power supply of EC is generated

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In this lesson, let's take a look at the clock, reset, program of EC...how these conditions are met

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First of all, after the EC receives power from AVCC, VSTBY, etc.,

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before it is reset, the EC will open-drain and output S5_ENABLE

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Because S5_ENABLE is provided by the GPIO pin inside the EC chip

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Before the GPIO pin is reset and the program is not read, it is in a high-impedance state

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Then S5_ENABLE is powered by EC standby in the circuit and is pulled up to high level

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Therefore, when the EC open-drain outputs S5_ENABLE, this signal is a high-level signal

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Then, S5_ENABLE is renamed to 3V_5V_EN through a resistor, and then renamed to

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PWR_5V_EN1 and PWR_3D3V_EN2

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They came to the EN1 and EN2 pins of PU4501 respectively,

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which are used to control the generation of two PWM outputs

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The PWM on the left is PWR_3D3V, which is renamed 3D3V_S5 after passing through the node

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The road on the right is PWR_5V, which is renamed 5V_S5 after passing through the node

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3V_5V_EN is controlled by PURE_HW_SHUTDOWN# through diode

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This PURE_HW_SHUTDOWN# signal comes from the over-temperature protection circuit

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This signal will be pulled down by the temperature control circuit only if there is overheating after starting up

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When this signal is low level, it will pull down the turn-on signal (3V_5V_EN) to low level along the diode

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When the start signal is low level,

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the two PWM outputs will be turned off to realize the power down of the whole machine

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After 3D3V_S5 and 5V_S5 are generated normally

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This 3D3V_S5 will provide power to U2502 (BIOS chip), and then the EC delay will be reset

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The external name is ECRST##

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Search for the source of this reset signal and find that it comes from the pull-up of the EC standby power supply

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This EC has a built-in clock crystal oscillator, no need to provide an external standby clock

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When the EC is powered and reset,

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then the EC reads the BIOS through the SPI bus and configures the GPIO pins of the EC

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All GPIO pins of EC need to be defined by the program

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For example, the SYS_PWROK power good signal sent by EC

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Before the EC reads the program and configures the pin, this pin has no function

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When the EC reads the program and configures the pins, the EC can work normally

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OK, this is the standby condition for the EC