As with any acid, it brings down both pH and TA together, though the pH drops more than the TA. This assumes you are using Trichlor for a while so there is chlorine usage/consumption. For example, adding 3 Trichlor tabs/pucks to a 10,000 gallon pool starting out with a TA of 100 ppm and pH of 7.5 would end up with a pH around 7.0 and a TA of 88 ppm. In practice, the pH might not drop that much since there will likely be outgassing of carbon dioxide during that time. The cumulative FC added and presumably consumed is 16 ppm and the CYA increase is 10 ppm.

Don't forget that for every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.

Richard