Signals and Buses
I2C, SMBus, SPI, eSPI, PCIe, USB, eDP and the control signals that bring a board to life.
- Active-Low SignalAn active-low signal does its job when it is pulled to 0 V. Schematics mark it with #, _N, _L or a bar, as in PLTRST# or PWRBTN#.
- eSPIeSPI (Enhanced Serial Peripheral Interface) is the bus between the chipset and the embedded controller on modern Intel and AMD laptops, replacing the older LPC bus.
- Open-Drain OutputAn open-drain output can only pull a line low; a pull-up resistor makes it high. Power-good, reset, interrupt and SMBus lines on laptop boards work this way.
Guides on this topic
- How to Use a Schematic and a Boardview TogetherReading Schematics · 6 min
- Beep and Blink Codes: How to Use Them in Board DiagnosisDiagnostics · 6 min
- USB-C Laptop Not Charging: PD Controller DiagnosisDiagnostics · 6 min
- Unpopulated Components (NC, DNI, @) in Laptop SchematicsReading Schematics · 6 min
- Test Points in Laptop Schematics and How to Use ThemReading Schematics · 6 min
- Schematic Revisions: Why Rev 0.3 vs Rev 1.0 MattersReading Schematics · 6 min