169 (NORD-1 card)

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169 Cambridge control, is a card that is used in the NORD-1 CPU.

Component side.
Solder side.

It is a controller for interfacing the EXPANDARAM-18 core memory.

Introduction

The card is made in the standard NORD-1 card format.

CPU model Crate position
29
35 C31

The logic diagram is documented in drawing 2A69.[1]

Switches and indicators

There are no switches or indicators on this board, but there is a strap field on the front. The four top positions are grounded and the four inputs have pullups.

Counting from the top :

  • MT4 Goes to the edge connector 45 (MCIR0) but is also used internally on the card. This signal is also controlled by the MC0 signal from the edge connector 49.
  • MT3 (Test I/O) : Goes straight to the edge connector 55 (MT30)
  • MT2 : Goes straight to the edge connector 54 (MT20)
  • MT1 (Repeated single) : Goes straight to the edge connector 53 (MT10)

Function

Preliminary : The function seems to be to translate and ensure the timing of the control signals are correct. To do that it uses four JK-flip-flops (74107) and two one shots (74121) along with logical gates.

The card has a free running oscillator at about 2.5 MHz consisting of four inverters (3C) and RC circuits.

BOM

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

  • 2 x 7400 quad 2-input NAND gate
  • 1 x 7401 quad 2-input NAND gate with open collector outputs
  • 2 x 7402 quad 2-input NOR gate
  • 5 x 7404 hex inverter
  • 3 x 7410 triple 3-input NAND gate
  • 2 x 7420 dual 4-input NAND gate
  • 5 x 7440 dual 4-input NAND buffer
  • 1 x 7450 dual 2-wide 2-input AND-OR-invert gate (one gate expandable)
  • 2 x 74107 dual J-K flip-flop with clear
  • 2 x 74121 monostable multivibrator

Reference

  1. HARDWARE MANUAL NORD 1