Using v2 Firmware on v1 MarcDuinos

Wiring Diagrams, v1 Boards running v2 Firmware

It is possible to run v2 firwmare on v1 boards, with a slight modification to the connections. 
v2 Firmware is available here. It adds I2C support, for the REON Holos in particular.
Just follow the diagrams below (click on the pictures to make them bigger):

Master:

Slave:

Short Story

To run v2 firmware (instead of v1 firmware) on v1 boards:
On the master
- Connect Sound on pin PC1 instead of PC4
On the slave
- Connect Lights on pin PC1 instead of PC0
This liberates pins PC4 and PC5 for I2C usage (PC4 is SDA and PC5 is SCL).

For now that's all you need as the rest is not used officially, and is already reflected in the diagrams above.

Long Story

Pins assignments have been switched around in the v2 firmware to liberate the I2C pins and allow for future extensions. To run v2 firmware on the v1, you to connect pins slightly differently.

Pin assignments on the Master:

 Pin  v1 Firmware
 v2 Firmware
 Notes
 PC0  Slave Out
 Slave Out
 No Change
 PC1  Not Assigned
 Sound Sound output moved to PC1 in v2
 PC2  Not Assigned
 AUX1  Future Use
 PC4  Sound  I2C SDA  New I2C functionality in v2
 PC5  Not Assigned
 I2C SCL  New I2C functionality in v2
 PD7  Not Assigned
 AUX2  Future Use
 ADC6  Not present on v1 hardware  AUX3  Future Use
 ADC7  Not present on v1 hardware  AUX4  Future Use

Pin assignments on the Slave:

 Pin  v1 Firmware
  v2 Firmware Notes
 PC0 Lights Slave Out Slave out moved to PC0 on v2
 PC1 Not Assigned Lights Lights output moved to PC1 in v2
 PC2 Not Assigned AUX1 Future Use
 PC4 Slave Out I2C SDA New I2C functionality in v2
 PC5 Not Assigned I2C SCL New I2C functionality in v2
 PD7 Not Assigned AUX2 Future Use
 ADC6 Not present on v1 hardware AUX3 Future Use
 ADC7 Not present on v1 hardware AUX4 Future Use