I am looking for a DAC that does not require a clock to update its output. Parallel input (8 bits is sufficient), single supply (3.3 or 5 V), voltage output (rail to rail preferred), any speed, internal reference. I would like its output voltage to continuously track and change whenever any of its inputs changes. I have seen this referred to as a transparent DAC.
The AD7801 seems to come close. It could be operated in Automatic Update Mode by tying LDAC to GND but then WR still needs to be clocked.
A clock is very important to a converter. It is used to tell the part when to consider the data to be valid or not. Without it, the part should still have a way to tell whether the data that is sent to the register are valid or not. One way is to use manchester coding.
I could imagine DAC's using manchester coding but unfortunately ADI do not have clockless DACs. You are correct on the AD7801. You may also take a look at ADI's DAC8562.