On 12/01/2011 12:30, Peter wrote:
Malcolm Lear wrote:
I was looking at the QL schematics a few weeks back and noticed the
Microdrives use a serial bus. I guess this is bit banged by the software
to transfer data. Could this be connected to the SD SPI serial interface
using level shifters (5V - 3.3V)?
As always, things are not that easy :-)
I'd have to leave at least 3 of 6 lines in their original use (drive
selection) so other microdrives don't get totally confused.
The other three lines are just one output and two data lines (both seem to
change their direction at the same time, according to that output). And I
don't know wether the data lines can be bit-banged at all.
Even if I construct something useful from those 3 lines - which would of
course involve more that just level-shifting - there is still risk to
confuse the microdrive portion of the OS.
Speaking from pretty little low level knowledge, how about abandoning
the microdrives completely (I thought you were) and making your
interface emulate microdrives? I wonder what the O/S would make of a
giant sector count (8-)#
I suppose speed would be an issue as well. I wonder whether the 8302
could input/output faster. I know Laurence wound up the data lines to
the 8749 to a remarkable degree. We never found an upper limit as it
could clearly go faster than the PIC. It was so fast that it took a
long time for us to realise we *were* getting a response. I still have
the polaroids somewhere taken on my oscilloscope.
Tony
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