The logic diagram of the counter is shown in Fig. 6. I6(a ). Since there are two unused stales,
we analyze the circuit to determin e their effec t. If the circuit happens to be in stare 0 I I because
of an error signal, the ci rcuit goes to state 100 after the application of a clock pulse. Thi s action
may be determined from an inspect ion of the logic diagram by noting that when B = I. the
next clock edge complements A and clears C to 0, and when C = I, the ne xt clock edge complements
B. In a similar manner, we can evaluate the next state from present state II I to be 000.
The state diagram includ ing the effec t of the unused states is shown in Fig. 6. I6Ib ). lfthe circuit
ever goes 10one of the unused slates because of outside interfe rence, the next count pulse
transfers it to one of the valid states and the circuit continues to coo nt correctly. Thus. the counter
is self-correcting. In a self-correcting counter, if the counter happens to be in one of the unused
states , it eve ntually reaches the nonnal count sequence after one or more clock. pulses.
The logic diagram of the counter is shown in Fig. 6. I6(a ). Since there are two unused stales,we analyze the circuit to determin e their effec t. If the circuit happens to be in stare 0 I I becauseof an error signal, the ci rcuit goes to state 100 after the application of a clock pulse. Thi s actionmay be determined from an inspect ion of the logic diagram by noting that when B = I. thenext clock edge complements A and clears C to 0, and when C = I, the ne xt clock edge complementsB. In a similar manner, we can evaluate the next state from present state II I to be 000.The state diagram includ ing the effec t of the unused states is shown in Fig. 6. I6Ib ). lfthe circuitever goes 10one of the unused slates because of outside interfe rence, the next count pulsetransfers it to one of the valid states and the circuit continues to coo nt correctly. Thus. the counteris self-correcting. In a self-correcting counter, if the counter happens to be in one of the unusedstates , it eve ntually reaches the nonnal count sequence after one or more clock. pulses.
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