Note that we are not currently sure if the new pin 27-40 PWM1, GPCLK1 and GPCLK2 peripheral pin functions will be made accessible under Raspbian and if so which pins they will be assigned to, hence the duplicated pins shown with these functions.

Lost From The Model B Rev 2 Board

The P5 connector is not present on the new Model B+ board and its pins have not been moved to the new J8 connector,.  This means the loss of the 2nd I2C port (although this peripheral is available via the display and camera FFC connectors – TBC if this is easy to enable for general use under Raspbian).  The pins that are no longer present via a header are:


3.3V Output

External circuitry may draw up to a total of 50mA max current from the 3.3V Out pins (true for Model B so presumably true for Model B+ but not confirmed as full schematic not yet available).

Is maximum current from 3.3V pin really 50mA?

IO Pins

All IO pins are 3.3V, not 1.8V.  Pins are not 5V tolerant.

Full details are available here

Max Current

Maximum 16mA per IO pin (sink or source) with the total current from all pins not exceeding 51mA  (true for Model B so presumably true for Model B+ but not confirmed as full schematic not yet available). See a detailed explanation here.

Power-up State

Its likely all pins are set as inputs on power up (TBC).

I2C pins (e.g. Pj-3 and P8-5) are therefore high due to the pull up resistors on these pins.

Pull-Up & Pull-Down resistors

The GPIO ports include the ability to enable and disable internal pull-up or pull-down resistors from code.

Pull-up is 50K min – 65K max.

Pull-down is 50K min – 60K max.


1K8 pull up resistors are included on the RPi board so are not needed externally (true for Model B so presumably true for Model B+ but not confirmed as full schematic not yet available).

Interfacing the RPi 3.3V I2C pins to a 5V device like an Arduino – see here.


The Chip Select signals are for up to two independent slave devices.  It seems that with the SPI port enabled in Raspbian both the CS0 and CS1 pins are assigned to it and therefore can't be used as IO (our assumption – correct?)


The PWM pin available on the GPIO header is shared with the Audio system  (true for Model B so presumably true for Model B+ – not confirmed as full schematic not yet available). This means that you can't use the PWM output and play audio through the 3.5mm jack at the same time.

3.3V / 5V Interfacing

See our other page here

ID_SD & ID_SC Pins

These are for an auto configuration eeprom which you can include on your RPi add on board and which Raspbian will read to detect the board connected.  For more info see here.




We benefit hugely from resources on the web so we decided we should try and give back some of our knowledge and resources to the community by opening up many of our company’s internal notes and libraries through mini sites like this. We hope you find the site helpful.
Please feel free to comment if you can add help to this page or point out issues and solutions you have found, but please note that we do not provide support on this site. If you need help with a problem please use one of the many online forums.


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