Counters and Registers
455
Figure 11.41 Timing waveforms of IC 74166.
11.12.5 Bidirectional Shift Register
A bidirectional shift register allows shifting of data either to the left or to the right. This is made
possible with the inclusion of some gating logic having a control input. The control input allows
shifting of data either to the left or to the right, depending upon its logic status.
11.12.6 Universal Shift Register
A universal shift register can be made to function as any of the four types of register discussed in
previous sections. That is, it has serial/parallel data input and output capability, which means that it can
function as serial-in serial-out, serial-in parallel-out, parallel-in serial out and parallel-in parallel-out
shift registers.
IC 74194 is a common four-bit bidirectional universal shift register. Figure 11.43 shows the logic
diagram of Ic 74194. the device offers four modes of operation, namely (a) inhibit clock, (b) shift
right, (c) shift left and (d) parallel load. Clocking of the device is inhibited when both the mode control
inputs S 1 and S 0 are in the logic LOW state. shift right and shift left operations are accomplished