It doesn't work the same way as TMS1000. Instead of outputting all segments at once, it updates digits per-segment. This way, it's possible to make a digit partially blank.
It's not that simple. There are 2 PLAs involved, the segment PLA and output PLA. The chip checks for a coincidence between the two to determine whether or not a digit should be updated.
For details, see TI-30 patent description of fig.13
