next up previous contents
Next: Edge Triggering Up: Dynamically Clocked Flip-Flops Previous: Dynamically Clocked Flip-Flops

Master/Slave or Pulse Triggering

We can simulate a dynamic clock input by putting two flip-flops in tandem, one driving the other in a master/slave arrangement as shown in figure 7.23. The slave is clocked in a complementary fashion to the master.

Figure 7.23:  An implementation of the master/slave flip-flop.

This arrangement is still pulse triggered. The data inputs are written onto the master flip-flop while the clock is true and transferred to the slave when the clock becomes false. The arrangement guarantees that the outputs of the slave can never be connected to the slave's own RS inputs. The design overcomes signal racing (ie. the input signals never catch up with the signals already in the flip-flop). There are however a few special states when a transition can occur in the master and be transferred to the slave when the clock is high. These are known as ones catching and are common in master/slave designs.

Doug Gingrich
Tue Jul 13 16:55:15 EDT 1999