Back plane and Board size

I've decided to go for DIN 41612 96 way connectors for the back plane. I've also decided upon having two connectors per board. This will allow the provision of a 32-bit address bus and a 32-bit data bus. Although the CPU will only use 16 data bits for now.

The hardware specification follows the theme of the NuBus.

The board depth will be 220 mm as standard. Allowing the use of a 235 mm sub-rack.

The board height will follow the IEC standard and be 6U ( 100 mm + (6/3 - 1) * 5.25" = 233.35 mm (9.19").

The 41612 connectors will be centered 50 mm from each board edge, and 5.25" center to center.

For the back plane the Harting 0903 296 6825 socket (Farnell #1096910) will be used.

For the cards the Harting 0903 396 6921 right angle plug (Farnell #1096950) will be used.

The back plane will be housed in a Schroff 24563-432 6U 235 mm sub-rack (Farnell #1455791).

Following will also be required:

Assembly kit 21100-435
Guide Rail 220 mm deep 24560-353
Torx panhead screw 2.5 * 9.3 mm 24560-141

Card spacing in the back plane will follow NuBus as 0.8". Maximum component height will be 13.97 mm. The maximum component lead length below the board will be 2.54 mm. The maximum bus length will be 13.2", allowing 16 card slots.

Clock termination will be 120R/180R at the far end, and address control lines will be terminated at both ends by 270R/470R.

Having a 32-bit address bus gives a maximum memory of 4GB, well enough. The top 256MB will be allocated as private to the slots, 16MB per slot. Back plane will provide each card with the ID number of the slot (0-15). The higher the number, the higher the slot priority.

There will be no top cover for the sub-rack, and so nothing to interfere with the cables up to the console PCB. The console PCB will be mounted on the back of a 3U front panel.

What a fixed up set of units, that is what you get by using standard parts.

 Doesn't sound much but that all took a whole day to work out.

Scope is here!

The scope is here, and it works fine. The photo shows the testing of the switch debounce circuit. The ATX bench power supply can be seen to the right of the picture.

The rack cabinet has been ordered, as have the base chips for the ALU. I've also ordered at extreme cost the pro version of Eagle. Have to have the pro version due to the size of the back plane PCB.

Underway

Well the project is finally underway, I fully expect this project to take several years, but it will be fun. I ordered an oscilloscope+logic analyzer earlier this week from Germany, should be here in a couple of weeks. I've also ordered some bits from Farnell to convert an ATX power supply into a bench power supply.

Have downloaded the free version of Eagle (a schematic and pcb development package), and have found BatchPCB on the web. BatchPCB seems reasonable price wise, so looks like I can avoid having to wirewrap everything.