Controling mode of PCIe parallel ports

My x64 port of InpOut32
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Controling mode of PCIe parallel ports

Post by Zaaphod »

zI'm wondering if anyone has figured out how to get modern PCIe parallel ports into specific modes (spp, ps/2, epp, ecp) I am baffled by this, just when I think I figured out what is going on, suddenly I can't duplicate my results. I have searched all over the web for documentation and the closest I can find is the link here:

All I want to do is force the port to be in a mode compatible with original ISA parallel ports. I am able to output to D0-D7 reliably, and I can change direction and read data in from D0-D7 reliably, the place where strange things are happening is with the 4 bits used with the control port. Pins 1, 14, 16, & 17 I have managed to get these 4 pins to behave in 4 distinctly different ways, some expected, others not. Here is a summary of how they behave.

1. Outputting a Low
2. Input with pullup
3. Input with Pulldown
4. floating, but latches to either high or low and retains the last state when floating.

The original ports used to act like #2, but I can only rarely get the PCIe ports to behave this way, and to do so, I need to output 0xFF on D0-D7, making them useless for output. I've been trying all kinds of methods of writing to the other control bits, including the ones labeled as unused, which do end up changing the mode of these pins. Sometimes if I write 0xD4 to the control port, it will act like #2, regardless of D0-D7 and if I write 0x04 to the control port, it will work like #4. I've been going around and around in circles trying all kinds of things including writing to the extended control register... but just can't figure out what's going on and can't find any good documentation on this. If anyone has any ideas it would be greatly appreciated.

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