Why so many numbers for the same thing?

Wiring PI Pin Number BCM Pin Number Header pin number Header pin number BCM Pin Number Wiring PI Pin Number   3.3v 1 2 5v   8 BCM 2 (SDA) 3 4 5v   9 BCM 3 (SCL) 5 6 Ground   7 BCM 4 (GPCLK0) 7 8 BCM 14 (TxD) 15   Ground 9 10 BCM 15 (RxD) 16 0 BCM 17 11 12 BCM 16 (PWM0) 1 2 BCM 27 13 14 Ground   3 BCM 22 15 16 BCM 23 4   3.3v 17 18 BCM 24 5 12 BCM 10 (MOSI) 19 20 Ground   13 BCM 9 (MISO) 21 22 BCM 25 6 14 BCM 11 (SCLK) 23 24 BCM 8 (CE0) 10   Ground 25 26 BCM 7 (CE1) 11 30 BCM 0 (ID_SD) 27 28 BCM 1 (ID_SC) 31 21 BCM 5 29 30 Ground   22 BCM 6 31 32 BCM 12 (PWM0) 26 23 BCM 13 (PWM1) 33 34 Ground   24 BCM 19 (MISO) 35 36 BCM 16 27 25 BCM 26 37 38 BCM 20 (MOSI) 28   Ground 39 40 BCM 21 (SCLK) 29

Legend Power Common SPI (Serial Peripheral Interface Bus) I2C (Inter-Integrated Circuit) Serial Pulse-width-modulation

• The BCM2835 C library uses the header pin numbers
• The PHP library uses the BCM numbers

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