Re: [CAD_CAM_EDM_DRO] EMC, ISA and other Questions...

----- Original Message -----
From: Jon Elson <elson@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Wednesday, January 22, 2003 2:17 AM
Subject: Re: [CAD_CAM_EDM_DRO] EMC, ISA and other Questions...


>
>
> alex wrote:
>
> >OK, thank you very much for the explanation.
> >I was looking at the C code of EMC but from the controller end of it.
> >the reason I'm interested is because I want to mate DOS powered nodes
with
> >the central node, running EMC interpreter.
> >Why I like DOS - not because I'm fond of typing away, but because it
gives
> >an ability of easy control of the hardware. In fact with Debug you can
pry
> >it
> >up to the limit. I still cannot quite figure out , Jon, how you were able
> >to control so many devices from the parallel port, given limited
> >availability
> >of the address lines.
> >
> There are no address lines. The RS-1284 spec renames the control lines
> to be Write/, AddrStrobe/
> and DataStrobe/. So, the 8 bits on the data lines when AddrStrobe/ goes
> low becomes the address
> to read/write data from. In this particular setup, it was most
> advantageous to read or write
> consecutive bytes, so I made the address counter in the devices count up
> after each data transfer.
> So, I have 256 possible device registers to talk to.
>
> > On the other hand, little DOS modules will give an
> >access
> >to ISA bus with huge number of addresses.
> >
> >
> Trying to keep a bunch of processors synchronized to the millisecond
> level is not an easy
> thing to do. I think keeping it down to ONE CPU is a great
simplification.
>
> Jon
>
>
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