The 32-bit counter counts up or down synchronously with the Source signal. The Gate signal and other counter inputs are asynchronous to the Source signal, so the cDAQ chassis synchronizes these signals before presenting them to the internal counter.

Depending on how you configure your chassis, the cDAQ chassis uses one of two synchronization methods: 80 MHz Source Mode or External or Internal Source Less than 20 MHz.

80 MHz Source Mode

In 80 MHz source mode, the chassis synchronizes signals on the rising edge of the source, and counts on the third rising edge of the source. Edges are pipelined so no counts are lost, as shown in the following figure.

Figure 79. 80 MHz Source Mode

External or Internal Source Less than 20 MHz

With an external or internal source less than 20 MHz, the module generates a delayed Source signal by delaying the Source signal by several nanoseconds. The chassis synchronizes signals on the rising edge of the delayed Source signal, and counts on the following rising edge of the source, as shown in the following figure.

Figure 80. External or Internal Source Less than 20 MHz