Monday, 27 February 2012

Shit Register Counters


Shift register counters:
Shift register with a feedback connection can behave as a counter.
Ring counter:
 
The Sout output of SISO register is connected to Sin input of register. The register should initially loaded with any one flip-flop having logic ‘1’. So this is called circulating 1 counter. If the register is loaded with any flip-flop having 0 and remaining all 1’s, then such a counter is called circulating ‘0’ counter.
 The no. of states is equal to the no. of flip-flops in register.
This is not a self starting counter. Because the contents of register may be all 0’s or all 1’s. Then on each clock edge the contents of register can’t change, thus there is no change of state.

Johnson Counter:
 
The complement of Sout output of SISO register is connected to Sin input of register. This is self starting counter.  If no. of flip-flops in register are n, the no. of state in counter are 2n. 

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