No such function exists. No such function can exist, as it would require that digital CPUs be able to store and process infinitely precise analog signals until they were converted to digital form on command.
If you need to convert an analog signal to a digital signal, you need an analog to digital converter, after which the task becomes one of reading the digital values from the device. There are several functions for reading values from devices as different devices have different communication protocols. The Instrument Control Toolbox supports several communications protocols.
