2.2.1 Aliasing

Device Alias ID refers to the alternate 7-bit address assigned to either the serializer, deserializer, or remote slave. The Device Alias can help differentiate devices that have the same Device ID or physical I²C address. TI recommends that the I²C master always use the device alias to communicate with a remote I²C slave.

For example, the DS90UB954-Q1 can support two serializers like the DS90UB953-Q1. If both serializers are 953s that house the same camera, the device IDs and default alias IDs for the corresponding devices will be the same. As a result, the best practice is to write a unique alias ID to each device. Note that these conventions only apply when the I²C passthrough is enabled. Refer to Section 2.3 on I²C passthrough for more information.

I²C addresses are always 7 bits (binary). The majority of the registers on the DS90UB95x-Q1 associated with I²C addresses uses bits [7:1] for the address, and bit 0 is either reserved or used for some other purpose. Therefore, while loading an address value to a specific register, it is always left-shifted by 1 bit. For example, 0x50 (101 0000) left-shifted by 1 bit is 0xA0 (1010 0000). This operation can be represented as, 0x50<<1 which is equal to 0xA0.

If a defined alias ID does not follow this convention, problems can arise. For example, register 0x5C on the 954 holds the SER_ALIAS_ID. If bit [0] of the 8-bit address is set to 1, transactions using this alias ID will be automatically acknowledged. As a result, the controller (or master) sends the slave address and does not listen for a response from the slave when communicating with the serializer on the bus. All writes are attempted regardless of the forward channel lock state or status of the remote Serializer Acknowledge. This can be problematic when validating the link between the SER and DES.