SN74F161AD

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The SN74F161AD is a 4-bit synchronous binary counter with a preset feature. It counts up or down on the rising edge of the clock input. The counter has independent clock inputs for up-counting and down-counting. It is implemented with a carry lookahead circuit allowing cascading the counter stages while maintaining high performance. The preset capability allows load in a desired count from an external source without resetting the counter or having to wait for the counter to count up to the desired setting.

The SN74F161AD contains four independent triggers for UP/DOWN counting. The UP/DOWN clock input is used to control the direction of the count sequence. A low-to-high edge of U/D causes the counter to count up, low-to-high edge causes the counter to count down. The UP/DOWN count enable is used to enable or disable the U/D inputs. When enabled the counter counts with an active U/D input. When disabled, the counter count is arrested.

The SN74F161AD has a priority in logic. In the case of two inputs in conflicting conditions at any clock edge, the highest priority input is latched. The priority is given as: Load < Up/Down Enable < Down < Up. The output of the counter is synchronized to the system clock by a carry lookahead circuit.

The three state output buffers permit direct connection to bus-oriented systems. Pulled-up outputs of the buffer are designed to be compatible with standard TTL drive circuits. These buffer also have the capability of driving up to 15 LS-TTL loads and allow for easy interfacing to TTL/CMOS circuits.

The SN74F161AD includes a loading feature with a parallel load (PL). The PL input latch transfers the data from input pins DI0 to DI3 to the outputs (Q0 to Q3) of the counter upon the positive-going edge of the PL input pulses. To ensure that loading does not change the state of the counter, the PL pulse must be delayed for the appropriate time period, about 0.4 μs, after both UP/Down and U/D enable goes low. The up/down functionality is unaffected by the loading feature.

In conclusion, the SN74F161AD offers a wide range of applications in logic-based design, such as frequency divider, pulse width modulator (PWM), ripple counter, divide-by-pulse-width circuit, controllers, square raster display devices, division and digital frequency synthesizers. It is ideal for use in digital logic and a variety of control applications.

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