In the ViVA calculator, there's also the "getAsciiWave" function which will read simple multi-column data and convert it into waveforms.
As suggested above, the VCSV format is relatively straightforward; it's comma-separated-value with some additional header information in comments at the top of the file to give information about signal names, type of data, and so on - it provides more info for ViVA to know how to plot the data.
There is also the "psf" utility to convert psf format data from ASCII to binary. However, constructing a file that looks like ASCII PSF is going to be a lot more work than using VCSV.
We also have an enhancement request to be able to directly open simple CSV files in ViVA - but it's not been implemented yet (it would need some kind of import UI to assign signals to columns, a bit like you get when you import a text file in Excel).