74161

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The 74161 is a 74-series logic 4-bit latch and upwards counter. All(?) known uses of it inside cartridges just use it as a latch.

74161 Pinout

              .--\/--.
     /Clear - |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| - /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.

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