Peter C. Wallace wrote:
> With the 9805, I can see that the strobe ends in response to my wait signal,
> but the data is sampled somewhere around the falling (leading) edge of the
> strobe. I thought about an error caused by the port seeing /wait asserted too
> early so even tried putting a fair sized cap at the parallel port end of
> /wait, this slowed the handshake, but did not help reading tha data at the
> right time. Only way I could thnk of making the NetMos cards read right is by
> supplying read data when READ is high, but thats too ugly (bus conflicts etc)
> to consider seriously.
I signed up for an account at MosChip.com, after that they let me see
their docs. Their FAQ for the 9805 says this:
MosChip 9805 FAQ:
> An additional problem exists with EPP Mode. We have identified a timing
> problem
> in the chip that affects reading data from the remote device in EPP Mode. We
> are
> able to write data to the device (printer etc.) just fine under all
> conditions. The
> problem only affects reading data back from the device (scanner etc.) in EPP
> Mode.
> The symptoms result in the same Byte of data being returned for every read
> request.
> This problem does not affect ECP Mode. For this reason we recommend PS/2 or
> ECP Modes for applications that require bi-directional data transfers.
So yeah, the manufacturer admits that their hardware is broken, not much
anyone can do about that... Unfortunately.
--
Sebastian Kuzminsky
One of my most productive days was throwing away 1000 lines of code.
-- Ken Thompson
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