I2C is a hardware bus specification that allows 2 or more integrated circuits to communicate over two wires plus ground. I2C was designed for closed systems where the electrical characteristics of all bus connections and participants are known beforehand. As an end user, this means you should acknowledge that I2C is not a hardened consumer-oriented technology and all use of I2C to connect the ER-301 to other devices is at your own risk. Using I2C exposes sensitive circuitry of the ER-301 to ESD risks so precautions must be taken when designing your I2C-connected system. It is best to think of it as a form of community-supported factory-enabled hacking.
In a nutshell, i2c requires 2 communication lines (SCL and SDA) plus 1 ground line. So there are 3 pins on the Teletype that need to be connected with a custom cable to 3 pins on the ER-301. Along the bottom edge of the ER-301, you will find an I2C header with 3 pins labeled as GND, SCL, and SDA. Please connect those pins to the same pins on the Teletype as follows:
- Teletype GND to ER-301 GND.
- Teletype SCL to ER-301 SCL.
- Teletype SDA to ER-301 SDA.
Note that the connections are all one-to-one with no crossovers.