Header Strips, LEDs, and Reset - Raspberry Pi Hardware Reference - page 19

PWR LED
This red LED simply indicates that the Raspberry Pi has power. Figure 3-1 shows that the
power LED is supplied from the 3.3 V regulator. 14 Consequently, the LED indicates only
that power is arriving through the 3.3 V regulator.
Figure 3-1. Power LED
The power LED indicator is not necessarily an indication that the power is good .
It simply indicates that power is present. The LED can be lit and still not have sufficient
voltage present for the CPU to operate correctly.
If there is any doubt about how good the power supply is, refer to the “Voltage Test”
section in Chapter 2, which has information about how to perform a voltage test.
FDX LED
This green LED indicates that the Ethernet port is operating in full-duplex mode.
LNK LED
This green LED indicates that the Ethernet port has an active link-level status.
10M or 10/100 LED
Model B Rev 1.0 had this LED incorrectly labelled as 10M . The correct label is 100, which
is found on Rev 2.0 boards. This yellow LED indicates that the 100 Mbit link is active
(otherwise, it is a 10 Mbit link).
Header P1
The Raspberry Pi includes a 13x2 pin strip identified as P1, which exposes GPIO pins.
This includes the I2C, SPI, and UART peripherals as well as the +3.3 V, +5.0 V, and ground
connections. Table 3-2 shows the pin assignments for the Model B, Rev 1.0 PCB.