HATs On for the Raspberry Pi

August 25, 2014 | 00:18
HATs On for the Raspberry Pi
HATs On for the Raspberry Pi

Arduino has its shields, the Beaglebone Black its capes and up until recently the Raspberry Pi just had expansion boards. The latest B+ version of the Pi comes with more I/Os increasing the pin count to 40 of which 26 are backward compatible with the original connector fitted to the A and B boards. Two of the extra pins ID_SC and ID_SD are data and clock lines to connect to a serial EPROM fitted to the expansion board, sorry HAT. The EEPROM holds the board manufacturer information, GPIO setup and a thing called a ‘device tree’ fragment – basically a description of the attached hardware that allows Linux to automatically load the appropriate driver.

Adafruit already have some prototype HATs in the pipeline which includes a servo driver board, a 2.2” TFT display and a prototyping board which is a HAT version of their Perma-Proto quarter size breadboard PCB containing its own ID EEPROM to create custom HATs. Providing the power limits are not exceeded a number of HATs can be stacked on an RPi.

This feature will simplify hardware interfacing to the RPi but the name is a bit puzzling; surely the most appropriate thing to go on top of a Pi would be a CRUST but I guess reverse engineering that acronym proved too difficult, so HAT it is, which incidentally stands for Hardware Attached on Top.

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