mvsticto
Posts: 1
Joined: Tue Aug 21, 2018 11:31 am

RPI POE hat and 40 pin header access

Tue Aug 21, 2018 11:41 am

Hi,

I just received the new POE hat, and it looks great. Very compact compared to other models. But I am a little bit confused with the 40 pin header connector. It looks like there is no - obvious - way to still use the pins of the main board when the hat is mounted? What am I missing here??
With the arduino and alikes, the shields/hats are always implemented with extension headers, so the pins can still be accessed easily. Why is it not the same with this POE hat?

Thanks,
Maarten

hippy
Posts: 6297
Joined: Fri Sep 09, 2011 10:34 pm
Location: UK

Re: RPI POE hat and 40 pin header access

Tue Aug 21, 2018 12:10 pm

mvsticto wrote:
Tue Aug 21, 2018 11:41 am
What am I missing here??
That HATs, by definition, are not stackable, and the POE HAT is indeed a HAT.

6by9
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 7578
Joined: Wed Dec 04, 2013 11:27 am
Location: ZZ9 Plural Z Alpha, aka just outside Cambridge.

Re: RPI POE hat and 40 pin header access

Tue Aug 21, 2018 12:45 pm

(I think technically it isn't a HAT as it hasn't got the ID EEPROM)

If you want access to the GPIOs then use an extra tall header such as https://thepihut.com/products/stacking- ... all-header,. The longer pins stick out through the holes of the PoE PCB. You'll need to find some alternate mounts as it will have increased the height between the two boards.
Software Engineer at Raspberry Pi Trading. Views expressed are still personal views.
I'm not interested in doing contracts for bespoke functionality - please don't ask.

ShiftPlusOne
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 6086
Joined: Fri Jul 29, 2011 5:36 pm
Location: The unfashionable end of the western spiral arm of the Galaxy

Re: RPI POE hat and 40 pin header access

Tue Aug 21, 2018 1:47 pm

You can use the extra tall headers on the POE HAT as well, but you'll need to add a 2x2 one for the extra pins as well.
hippy wrote: That HATs, by definition, are not stackable, and the POE HAT is indeed a HAT.
We cheated.

We put the 'EEPROM' on 0x51 instead of 0x50 and modified the firmware to cope with that. So it is indeed stackable with other HATS. It only uses the ID pins, so any other HAT should be stackable with it without conflicting pin states.
6by9 wrote: (I think technically it isn't a HAT as it hasn't got the ID EEPROM)
The attiny814 on it pretends to be an EEPROM. But yeah, it doesn't meet the currently published spec, since it's not on address 0x50.

User avatar
Paul Webster
Posts: 812
Joined: Sat Jul 30, 2011 4:49 am
Location: London, UK
Contact: Twitter

Re: RPI POE hat and 40 pin header access

Tue Aug 21, 2018 2:59 pm

We put the 'EEPROM' on 0x51 instead of 0x50 and modified the firmware to cope with that. So it is indeed stackable with other HATS. It only uses the ID pins, so any other HAT should be stackable with it without conflicting pin states.
Good to see ... and perhaps should have been in the technical specs and even announcement (or whenever that trick was implemented).

Does this now mean that other HATs can do the same thing with perhaps a jumper to select 50/51?

ShiftPlusOne
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 6086
Joined: Fri Jul 29, 2011 5:36 pm
Location: The unfashionable end of the western spiral arm of the Galaxy

Re: RPI POE hat and 40 pin header access

Tue Aug 21, 2018 4:30 pm

Paul Webster wrote:
Tue Aug 21, 2018 2:59 pm
We put the 'EEPROM' on 0x51 instead of 0x50 and modified the firmware to cope with that. So it is indeed stackable with other HATS. It only uses the ID pins, so any other HAT should be stackable with it without conflicting pin states.
Good to see ... and perhaps should have been in the technical specs and even announcement (or whenever that trick was implemented).

Does this now mean that other HATs can do the same thing with perhaps a jumper to select 50/51?
No, right now it's a one off cheat that will only work for this particular HAT.

Return to “General discussion”