You can use these clock and trigger lines to synchronize not only measurements but also analog and digital stimulus signals. A D flip-flop triggers two cards running at different clock rates. You can connect an external clock source to the clock inputs of two or more cards, which gets them to synchronously digitize their input signals. You can also connect a common trigger signal to the cards' external trigger inputs. When the cards receive the trigger signal, they simultaneously digitize their analog inputs.
Some applications require the synchronization of two clocks.
A test of the response of a fiber-optic photodiode is one such application. A manual pushbutton acts as the trigger for both cards. The acquisition starts on the first rising edge of the 100-kHz clock after the pushbutton is pressed. In this case, the skew produced by the propagation delay in the divider is insignificant. Many data-acquisition cards use a local bus to transfer clocks and triggers between cards.