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Bus Controller and the new Backplane

7/29/2009

The idea of adopting the VME bus (with modifications) never convinced me entirely although I've had accepted it as a fact. Two thing bothered me: The large amount of ground pins and the fact that I was adopting a standard used in  a non-standard way. Besides, what is the need? I don't plan to plug factory-made VME cards in the Heritage/1 nor to place Heritage/1 cards in a VME bus, so the adoption didn't seems very useful.

Yesterday, I decided to put an end to the insanity by making my own proprietary backplane. It is divided into two halves: Data Slots and Control Slots, as planned before. Data slots use 96-PINs DIN 41612 connectors. Control Slots use 120-PIN DIN 41612 connectors. I had the former since last week; the later was ordered today to Digi-Key.

Another important decision I made today was about the BUS CONTROLLER Card. This is a card interfacing both Data and Control slots. The problem I had with this card had to do with connectors; I simply don't want my cards (any card) to connect in any way but through the Backplane... I hate the idea of having ribbon cables coming from one card to the other taking "unofficial" paths.

I had imagined the Bus Controller as a double-card so it could have two connectors: one 96-PIN plugging in a Data Slot and one 120-PIN plugging in a Control Slot... but that never got to convinced me. The definite solution came suddenly while I was at work: a larger card with the two connectors in-line. This card will not be placed vertically aligned with the others but horizontally below (or behind). Problem is that the cards I have now (5.5x8 inches) are two small for two connectors. So what I did today was to order five larger cards: 9x6 inches. These cards will also be used for building the Backplane itself. And this gave me a much better idea of how the CPU frame will looks like.

I am very happy with all this, only that the cost is increasing. So far I have expended little more that $600... just in switches, connectors and prototyping boards!