Following on the heels of their Raspberry Pi 5 launch and some specifications for their RP1 all-in-one peripheral chip, the Raspberry Pi folks have now released an update to the HAT peripheral hardware specification reflecting the new model. Called the HAT+, it represents a major step forward with some significant changes.
Most visible will be changes to the mechanical specification, for while the original HAT specification was very rigid this new version is much looser. A HAT+ must only mate with the 40-pin connector, including the ID pins, and line up with only a single mounting hole compared to the four on the original. Electrically, a HAT+ must recognise the standby power state in which the 3.3-volt line is powered down while the 5-volt line remains active, while software-wise, there are changes to the content of the ID EEPROM including the ability to inform about stackable smaller HATs.
As the Arduino folks will no doubt tell you, the danger for the maintainers of a popular standard is that it risks becoming a victim of its own success, leaving it to ossify as it falls behind the cutting edge. For the Raspberry Pi, it must be a tight balance between keeping it up to date and not losing earlier models, and by our reckoning, they may just have achieved it.
We like how some have allowed multiple HATs, and we wonder if this will work — or will be made to work — with the HAT+. You usually think of HATs as having sensors or lights, but that isn’t always the case.
