Firmata: messages syntax

How can I understand a syntax of commands for arduino with firmata?

I was trying firmata sample patches in vvvv environment, setting port outputs and PWM works perfect, but I can't read digital input (pin state). I was changing direction of the ports for input, but vvvv reads nothing. I know about similarity to MIDI syntax, but which commads work with arduino+firmata directly? If I understood firmata reads and respose a two byte (command + data) packets.