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A project log for Magnetic Bubble Memory Makes a Comeback

An Old Attraction to Magnetic Bubble Memory leads to a 1Mbit Board for the SBC-85, 8085 based single board computer

CraigCraig 04/08/2020 at 21:510 Comments

The arrival of the Bubble Memory Board was soon followed by some miscellaneous items in the latest digikey order.  The board has been populated with all the sockets and discrete components then fired up with empty sockets.  Since the SBC-85 only provides +5V, the bubble board needs a 6W DCDC converter to generate the 12V required by the bubble set.  With all the power working, the board was then populated with the cheap chips and simple things like the address decoding tested.  

Preliminary tests have been on the bus interface, address decoding, power supply, low voltage supervisory, power fail, and reset.  Bubble systems require special consideration for power protection to protect data integrity during power loss.  While this board looks pretty good so far, I expect that under full power testing it is going to require additional bulk capacitors on both the +5V and the +12V to fully satisfy the power fail voltage decay rate.  The allowable decay is 1.1 V/ms for the +12 and 0.5V/ms for the +5 but, of course the +12V on the SBC-85 Bubble board is generated from the +5V so the +5V is the ultimately the limiting factor.

While there are still some preliminary tests to complete, am hoping to get the 7220 bubble memory controller installed and communicating today.  Meanwhile, the bubble support chips (below) are trying to decide who has to go first .

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