74160 counter

(Monday, August 30, 2010)

74160-3 synchronous counters


* reset and preset are both active-low
preset is also known as parallel enable (PE)
 
  • 74160 synchronous decade counter (standard reset)
  • 74161 synchronous 4-bit counter (standard reset)
  • 74162 synchronous decade counter (synchronous reset)
  • 74163 synchronous 4-bit counter (synchronous reset)
These are synchronous counters so their outputs change precisely together on each clock pulse. This is helpful if you need to connect their outputs to logic gates because it avoids the glitches which occur with ripple counters. The count advances as the clock input becomes high (on the rising-edge). The decade counters count from 0 to 9 (0000 to 1001 in binary). The 4-bit counters count from 0 to 15 (0000 to 1111 in binary).
For normal operation (counting) the reset, preset, count enable and carry in inputs should all be high. When count enable is low the clock input is ignored and counting stops.
The counter may be preset by placing the desired binary number on the inputs A-D, making the preset input low, and applying a positive pulse to the clock input. The inputs A-D may be left unconnected if not required.
The reset input is active-low so it should be high (+Vs) for normal operation (counting). When low it resets the count to zero (0000, QA-QD low), this happens immediately with the 74160 and 74161 (standard reset), but with the 74162 and 74163 (synchronous reset) the reset occurs on the rising-edge of the clock input.
Counting to less than the maximum (15 or 9) can be achieved by connecting the appropriate output(s) through a NOT or NAND gate to the reset input. For the 74162 and 74163 (synchronous reset) you must use the output(s) representing one less than the reset count you require, e.g. to reset on 7 (counting 0 to 6) use QB (2) and QC (4).
Connecting synchronous counters in a chain
The diagram below shows how to link synchronous counters such as 74160-3, notice how all the clock (CK) inputs are linked. Carry out (CO) is used to feed the carry in (CI) of the next counter. Carry in (CI) of the first 74160-3 counter should be high.


Posted in Posted by vikas varshney at 11:47 AM  

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