The new and improved Programmer Shield is essentially a USB-JTAG
converter that gives advanced users complete access to the Photon's
memory space. It supports openOCD and the WICED SDK, and is built
around the FT2232H high speed USB FIFO.
Unlike the previous Programmer Shield, it is fully standalone and
requires no third-party programmers.
In addition to providing a JTAG interface, this shield can also act as
a USB to Serial converter. You can also use this shield as a generic
JTAG programmer for your other projects!
Designed for use with the Photon, backwards compatible with the Core.
Helpful Links @ particle.io:
* Datasheet 
* Common Issues 
* Device LED Codes 
* Device Ownership 
* Cloud Solutions 
* Common Questions 
* System Modes 
* Device Keys 
* Connectivity Help 
* Troubleshooting Tools