In case you need to implement your own client to talk to Pixy2 in a language or microcontroller we don't support, here is a handy reference of the Pixy2 serial protocol request and response packets.

For reference, our Arduino Library implements all of what's below in the files TPixy2.h, Pixy2Line.h, Pixy2CCC.h, and Pixy2Video.h. For consistency, the function names listed here are the same as in that implementation.

All values exchanged through the protocol are integer quantities (no floating point values). All quantities are either 1-byte (8-bit), 2-byte (16-bit), or 4-byte (32-bit). Multi-byte values are sent using little-endian byte ordering – that is, the least-significant-byte is sent first, followed by the next-least-significant-byte. The most-significant-byte is sent last. This page does a good job explaining endianness.

Furthermore, all signed integer quantities are represented using two's complement representation. This page describes two's complement representation.

It's not hugely important that you understand little-endian and two's complement representations – 95% of all processors use little-endian and two's complement. So you basically read the bytes into memory and tell the processor there's an integer there and it will happily interpret it correctly. But it's good to know, and required information for the protocol to work correctly.

Original Pixy would constantly broadcast data about objects it was (or wasn’t) seeing. With Pixy2, we’ve moved to a request-response system. That means Pixy2 is silent unless you send it a properly formatted request packet, in which case it will respond in kind.