Referring to the following Raspberry Pi 2 pinout chart:


I'm clear on all the pin functions except "GPIO_GCLK" (2nd function for pin 7), "SPI_CE0_N (2nd function for pin 24), and "SPI_CE1_N" (2nd function for pin 26).

I'm under the impression that GCLK is intended to be an output used to potentially clock another device, and that "CE" is short for chip enable or similar. I have a Microchip PIC and ATMEL background and these abbreviations are not used on those platforms.

Does anybody know of a good reference document that explains the purpose/function of GPIO_GCLK, SPI_CE0, and SPI_CE1? Any help would be much appreciated.

2 Answers 2


BCM2835 ARM Peripherals page 102 is probably the place to start.

I'm surprised that SPI CEx is confusing. SPI is a well known protocol available on many microprocessors including PICs and Atmels. CE (chip enable) is a synonym for SS (slave select).

GCLK (general clock) generate a general purpose clock (square wave of user defined frequency).

  • 1
    Just out of curiosity, can you give an example how one can use GPIO_GCLK to generate a certain frequency ? Also I don't think there is a lot of documentation about it to refer, nor it is implemented in standard GPIO libraries such as RPi.GPIO or wiringPi. Appreciate the help. Thanks. Sep 13, 2015 at 5:44
  • 1
    Python, C, command line all based on the C version in pigpio.c. Different code at Minimal clock access.
    – joan
    Sep 13, 2015 at 8:20

GPIO_GCLK appears to be one of a group that includes GPIO_GEN0 through GPIO_GEN7. Could possibly be a clock enabled GPIO pin set.

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