In the NORD-100 computer system all hardware modules are connected together via a common bus, the NORD-100 bus. All communication between NORD-100 modules is provided by this bus, except CPU, MMS and Cache communication. Therefore, the NORD-100 bus is general purpose, to allow all classes of NORD-100 modules simply to be "plugged" into the system.
The NORD-100 bus is available as a printed (card) backplane. The backplane is available in two versions containing either 12 or 21 positions for module connections. The two versions are otherwise equal.
Each NORD-100 bus backplane position contains a total of 96 lines (power and ground lines included).
The ND-100 bus may be divided into two logical parts
- 24-bit wide parallel multiplexed address / data lines
- control lines
The paired interrupt control lines (negative logic) INCONTR - OUTCONTR, INGRANT - OUTGRANT, INIDENT - OUTIDENT are connected OUTxxxx to INxxxx (daisy chain). The card position code lines PA0 - PA3 are connected to +5V and 0V like this:
- PA0:0, PA1:0, PA2:0, PA3:0 - card position: rightmost (furthest from the CPU)
- PA0:0, PA1:0, PA2:0, PA3:1 - card position: rightmost - 1
- PA0:0, PA1:0, PA2:1, PA3:0 - card position: rightmost - 2
in a binary sequence.
The PA0 - PA3 signal lines were previously used by memory cards, but are now no longer used.
All other signal and power lines are independent of card position.
NORD-100 card crates can be linked together via bus expander (BEX) modules. The number of crates to be lined together is set to a theoretical maximum of 8 crates.