ZN wrote:
If you understand the above (perfectly correct) description, congratulations.IIRC the romdisq uses a form of addressing similar to the miracle hard
disk where data is output on selected bits of the address line during a
second address cycle or something.
Exactly. _Any_ writing has to be roundabout.
The address is passed out serially (or maybe only bits 8 and above). The
data is then put on the databus. ... or something like that. I did not
see any documentation.
The ROM slot does not have a signal that would tell the hardware it is
supposed to write something, only read. To circumvent this, dummy reads are
performed into a part of the 16k ROM slot address space, and part of the
address (low 8 bits) is used as data. The actual address where the data is
written is selected by storing the state of the address lines using yet
another dummy read from a different part of the 16k ROM space. SH talked
with me about this at a meeting a long time ago, IIRC with RomDisq these
areas for dummy reads (and real reads when you actually want to read the
contents of the Flash) are 4k in size.
Stuart had that rare skill amongst hardware designers of knowing exactly the limits of what might be possible in software. Stems from the Sinclair principle - do not do anything in hardware that you can do in software.
Tony
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