Re: A little more information

["Shawn Dvorak" <rollinghillsobs@cfl.rr.com>]

Wouldn't you still need to do some clocking on the transfer over the
parallel port?  I'm not familiar with the workings of ECP ports so there may
be additional capabilities, but I have done some work with interfacing
devices using the old-fashioned parallel port.  There isn't any way to tell
when data is ready on the input lines on the port unless you add some other
control line that you would use as a strobe (either a "data ready" from the
Mark IV, or a "Send data" from the PC).

The Cookbook 245 CCD uses a simple implementation of the parallel port
transfer, sending only 4 bits at a time.  The rest of the bits (there are 12
or 13 actually available on a standard parallel port) are used for control.
These additional bits are needed since there's no brains or memory in the
CB245, so all of the A/D conversion and bit shifting to transfer the data a
nibble at a time has to be controlled from the PC.  The Mark IV is much more
sophisticated, but it seems that without some sort of clocking between the
devices you'd just be hoping that everything ran at the right rate, or you'd
end up with lost or duplicated bytes.

Shawn


----- Original Message -----
From: "Tom Droege" <tdroege@veriomail.com>
To: <aah@nofs.navy.mil>; <tass@listserv.wwa.com>
Sent: Wednesday, August 15, 2001 1:08 AM
Subject: Re: A little more information


> Arne,
>
> Oh! No you don't!  Talk me into feature creap that is.  ;^)  You won't get
> me attempting to add a serial IF into an existing system.  I know why you
> want it.  There must be serial to fiber optic converters on the market.
If
> you need such a device then that is the path I would choose.
>
> I have now looked at the parallel port, and it looks like all that is
> necessary is to rewire one end of the DB-25 cable.  Then write the DMA
> software that puts the event onto disk.
>
> Tom Droege
>
> At 08:32 PM 8/14/01 -0700, you wrote:
> >Bill/Tom's high-speed serial card is a reasonable solution
> >in that the approach is to take the parallel I/O data at the
> >Stamp end, convert it to serial for transmission, then convert
> >back to parallel using a PCI card.  I'd like to know how large
> >the FIFO is, what kind of handshaking is available, and how
> >elaborate a PCI interface was made.
> >   The real solution is to get rid of all copper between the
> >Mark IV and the host computer.  This means to use fiber and to send
> >the RS232 over the same link if it is bidirectional.  The RS232 stuff is
> >slow speed compared to the rest, but you have to break it out
> >at the Stamp end to make it look like a standard RS232 port plus
> >parallel port, unless you want major software work on the Stamp as well.
> >Since I raised my hand to work on the BX24 upgrade, we might
> >be able to add such support in the fancier chip.
> >   The PC printer port solution is ok if you use the ECP
> >protocol, since that can use DMA access and removes the typical
> >latency problem.  However, ECP protocol usually means additional
> >software on the Stamp end in order to handle the port negotiation.
> >Note that all of these solutions means work, which is why I'd
> >like to see some more effort put into the memory cards first.
> >Tom, you want to take data, not build another piece of hardware!
> >Arne
>
>
>