151 (NORD-1 card)

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151 is a card that is used in the NORD-1 CPU.

Component side.
Solder side.

It contains a free running oscillator and a state machine. It is reset by the Master Clear signal.


It is documented in drawing 2A51.

Switches and indicators

There are no switches or indicators on this board, but there is a 5 kOhm trimmer at the front that controls the frequency of the oscillator.


The oscillator runs freely but can be stopped by external signals (SP1 and MT7). WP9 from the operators panel (possibly HALT) can also block the oscillator.

The oscillator drives five JK flip-flops that counts up the state machine (16 states). According to the external signals NX and BK the state machine may loop or jump between states.

Signals coming out of this board is

  • TC0, TC1, TC2, TC3, TC4 - The internal state of the flip-flops
  • TM0, TM1, TM2, TM3
  • TX
  • TP0, TP1, TP3, TP5, TP7, TP9, TP11, TP13, TP15 - Outputs from the state machine

Most signals comes both in active high and low.


This list contains the logic circuits used, passive components are not listed.

  • 3 x 7400 quad 2-input NAND gate
  • 2 x 74H00 quad 2-input NAND gate
  • 1 x 7402 quad 2-input NOR gate
  • 7 x 7440 dual 4-input NAND buffer
  • 5 x 74H51 dual 2-wide 2-input AND-OR-invert gate
  • 5 x 74H72 AND gated J-K master-slave flip-flop with asynchronous preset and clear