What do the Canon hot shoe pins do, and is the protocol documented?
Asked 3/30/2019
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I’m trying to understand the signaling between Canon EOS cameras and Speedlite flashes beyond the basic center sync contact. For example, on a camera like the T6i with a Speedlite 600EX-RT II, what do the hot shoe pins do, and are the voltage levels, communication sequence, or protocol publicly documented? I know that shorting the center trigger contact to ground fires the flash, but I’m specifically asking about the additional Canon contacts and whether their behavior is known from official documentation.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
7y ago
2 Answers
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Canon considers their flash hotshoe pinout to be proprietary information and does not publicly post it anywhere. Companies like Godox make products by spending a lot of time and engineering expertise to try to reverse-engineer this type of communication protocol.
The only known signal is the one specified by the ISO standards for hotshoes/flash feet: the big center contact is sync, the rails are ground, and shorting the two is the signal to fire the flash.
And at any rate, the five contact/pin communication (and ISO compatibility) may become a thing of the past now that Canon has moved to their new multi-function hotshoe with the R3 and later bodies, which have contacts on the front edge of the foot plate/hotshoe, like Sony's multi-interface hotshoes/flash feet. And Canon's latest flash, the EL-5 has no pins on the bottom of its foot:
Originally by user27440. Source · Licensed CC BY-SA 4.0
user27440
3y ago
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Canon does not publicly document the full function or protocol for the extra hot shoe pins on its EOS/Speedlite system. Those contacts are considered proprietary, and third-party makers generally have to reverse-engineer them.
The only part that is standardized and generally known is the ISO hot shoe connection:
- center contact = sync/trigger
- shoe rails/ground = ground
- shorting center to ground fires the flash
That simple trigger signal does not by itself describe Canon E-TTL communication, data timing, or voltage details for the other pins. Public, official pin-by-pin signaling info for those extra Canon contacts is not generally available.
Also, Canon has been moving toward a newer multi-function hot shoe on newer cameras, so the older 5-pin arrangement may be less relevant going forward.
So the practical answer is: the center pin and ground are standard and understood; the rest of the Canon hot shoe communication is proprietary and not officially published.
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