Re: [CAD_CAM_EDM_DRO] Re: Caliper to PC interface, Part II: Data Format ?????? Help ?

krlux wrote:

>
> I've tested bidirectionality in ECP and EPP modes and have not got it to
> work. Do you have firsthand knowledge that they are bidirectional ? I've
> set up the control register for bidirectional operation but I can't get the
> pull up circuitry to disengage.

It is not just complicated, it is G*D D**N complicated. I had to go to the
web site for the maker of the floppy/parallel port chip on my motherboard
to figure the darn thing out. The registers that control the port are at the
usual 278 or 378 addresses, but the registers that set up the chip to
allow the extra modes and capabilites are at 401, I think. Anyway,
Once I found the right mode through BIOS settings, it did work, at
least in IEEE-1284 mode. This does handshaking of bytes in and
out, so you need external hardware to acknowledge each transfer.
But, I think you can set it to EPP mode and not use the ports that
cause the 1284 cycles. To set it for input, you need to set the 0X20
bit in the control register, for the 378 printer port, that would be
0X37A. Then, you should be able to read 8 data bits from the standard
data port 0X378. I found the ducument on the SMSC FDC37C665
series of chips to be very helpful in getting the last little pieces of info
together to make it work. See http://www.smsc.com/main/datasheet.html

>
> Agreed. Some of those modes are DMA driven, which would really be nice.

Unfortunately, using DMA from a user mode program in Windows (any
version) is practically impossible. I have tried - the problem is you
need a physical address to program into the DMA controller, and, although
people claim there's a way, I have never been able to get it to work.
It is not a parallel port problem, but a Windows problem to get an address
the DMA controller can use.

Jon