The DS90UB638-Q1 implements an I2C-compatible serial control bus. The I2C is for local device configuration and incorporates a bidirectional control channel (BCC) that allows communication across the FPD-Link cable with remote serializers, as well as with remote I2C target devices. The DS90UB638-Q1 implements an I2C-compatible target that can be compliant with the standard, fast, and fast-plus modes of operation. This allows I2C operation at up to 1-MHz clock frequencies. When paired with a DS90UB63x-Q1 serializer, the DS90UB638-Q1 supports a combined format I2C read and write access. The timing for the I2C interface is shown in GUID-5F07518C-A7AB-42F2-80DD-48E7FB195E52.html#SNLS506940.

For accesses to local registers, the I2C target operates without stretching the clock. Accesses to remote devices over the bidirectional control channel results in clock stretching to allow for response time across the link. The DS90UB638-Q1 can also act as I2C controller for regenerating bidirectional control channel accesses originating from the remote devices across FPD-Link. Set I2C_CONTROLLER_EN in register 0x02[5] = 1 to enable the proxy controller functionality of the deserializer.