This is how I understand it also.   Some have 'fixed' this issue by 
adding pull up resistors on certain pins.  If the port was set to EPP 
mode - this would not be needed.

(ie the g540 requires EPP mode for the charge pump to work)

sam

On 04/09/2012 06:25 PM, Peter C. Wallace wrote:
> On Mon, 9 Apr 2012, Sebastian Kuzminsky wrote:
>
>> Date: Mon, 9 Apr 2012 17:01:41 -0600
>> From: Sebastian Kuzminsky<[email protected]>
>> Reply-To: "Enhanced Machine Controller (EMC)"
>>      <[email protected]>
>> To: "Enhanced Machine Controller (EMC)"<[email protected]>
>> Subject: Re: [Emc-users] Hal_parport and EPP
>>
>> EPP mode is a completely different way of using the pins of the parport than
>> the regular SPP mode.  In SPP, you have programmatic control over the values
>> on the output pins, and you can read all the input pins.
>>
>> In EPP, those pins are driven by an additional piece of logic in the parport
>> controller.  The driver software asks the EPP controller to read and write
>> addresses on the EPP bus, and the controller twiddles the pins to implement
>> the software's request, according to the datalink protocol described by the
>> EPP spec.  So in order to do anything interesting/useful with the EPP port,
>> you need a second driver that knows what registers to read and write on the
>> device on the EPP bus.
>>
>> Simply switching the port to EPP mode doesn't accomplish anything.
>>
>> Maybe i'm missing something in your request?
>>
>>
>>
>>
>
> It does accomplish something subtle with some parallel port cards EPP mode is
> compatible with SPP mode but on some parallel port cards it changes the drive
> mode of some control output pins to Push-Pull instead of open drain with a
> pullup.
>
> Peter Wallace
> Mesa Electronics
>
> (\__/)
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