Developing About Braille Display with Voiceover

Hello, I'm undergraduate programmer in Korea. I'm developing Braille Display based iOS(specially iPhone) with Arduino & BLE. and I found that several finds of display are supplied technologies with Voiceover from Apple. I want to know specification & protocol between Braille display and iPhone, but I couldn't catch related information.

Is anyone who know about Library or protocol specification? 😢😢 Thank you.