74161

The 74161 (common variants 74LS161, 74HC161) is a 74-series logic 4-bit latch and upwards counter. Several discrete logic mappers use it as a latch.

74161 Pinout

              .--\/--.
     /Clear -o|01  16|-- +5V
      Clock --|02  15|-- CarryOut
         D0 --|03  14|-- Q0
         D1 --|04  13|-- Q1
         D2 --|05  12|-- Q2
         D3 --|06  11|-- Q3
CountEnable --|07  10|-- CarryIn
        Gnd --|08  09|o- /Load
              `------'

Signal descriptions

While /Clear is low, Q is reset to 0.

When CountEnable and CarryIn are both high, a low-to-high transition on Clock increases the value of Q by 1, wrapping from 15 to 0.

CarryOut is high when CarryIn is high and Q is 15.

/Load causes Q to be set to the value of D on a low-to-high transition of Clock.