Sunday, October 23, 2016

Connector built for new disk tool board, board looks good, also beginning tests of writing to disk


I managed to peel back the insulation and expose, then bend away the copper mesh that acts as a groundplane behind all forty of the signal lines in the ribbon cable. I could then trim it away leaving just the forty signal lines into which the vampire taps will connect.

Copper mesh groundplane peeled away from signal conductor ribbon
Groundplane trimmed back leaving an area to connect press-on IDC connector
I used a press-on IDC 40 connector, whose vampire taps will bite into the forty signal lines if I align it just right. I used my clamp tool that will squeeze the connector halves together. I had failed to get the lineup close enough on my first few tries, but today I ended up with no shorts and good connectivity to every signal line.

Clamping tool plus the two halves of the IDC connector

Connector on cable, ready to plug into the driver role extension board
If I had tried to substitute a plain 40 signal ribbon cable, it would have lacked the ground plane. The solution for many is to alternate ground lines between the signal lines, but that would have forced me to upscale to an 80 signal ribbon, a bit unwieldy, or switched to a large bundle of twisted pairs.

This cable gives a consistent 80 ohm impedance, important to handle the 3+ MHz signal generated to write clock plus data onto the drive. It must keep transitions within a 50 ns maximum interval, which is supported by high drive current and good termination.

I did work on the WriteSector logic and am preparing to run the logic analyzer to capture all the transitions I write, checking for a proper sector pattern. It will be painful, since what matters is the flip in state, not the absolute value of 1 or 0, and the relative timing of the flip compared to the 'clock' flips.

I will think a bit about how to best capture and test what occurs during the writing of a sector. 

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