The Integrated-Circuit D Latch (7475)
- The 7475 contains 4 transparent D latches with a common enable (gate) on latches 0 and 1 and another common enable on latches 2 and 3.
- When Q follows D (latch enabled) the latch is said to be transparent.
The Integrated-Circuit D Flip-Flop (7474)
- The 7474 is an edge-triggered device. The Q output will change only on the edge of the input trigger pulse.
- The small triangle on the clock (Cp) input of the symbol indicates that the device is positive edge-triggered.
- The D and the clock inputs are synchronous inputs.
- The set (SD) and reset (RD) inputs are asynchronous. They operate independent of D and Cp.
- The bubbles on the set and reset inputs indicate that they are low active.
The truth table for a positive-edge triggered D flip-flop shows an up arrow to remind you that it is sensitive to its D input only on the rising edge of the clock; otherwise it is latched. The truth table for a negative-edge triggered D flip-flop is identical except for the direction of the arrow.
