169 (NORD-1 card)

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.

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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.

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

• Hardware in NORD-1 Serial 47