[Linux-parport] Mode changes in Parallel Port

[Tim Waugh]

On Sat, Feb 21, 2004 at 07:38:05PM -0800, Ravi Shah wrote:

> What happens when we change the mode of the port from say SPP to
> Nibble or say SPP to ECP?

I think you are confusing different terms.

There is the transfer mode you are going to use, which is the method
(in terms of wire signals) by which you transfer data from one end of
the cable to the other: nibble is one such mode, and ECP is another.

Then there is the chipset mode (usually adjustable in the BIOS), which
controls the special features of the parallel port chipset.  Examples
are SPP for bare-bones functionality, 'bi-directional' for being able
to use the data lines in either direction, and ECP -- in ECP mode, the
chipset can be programmed to perform ECP data transfers in hardware.

So 'SPP vs nibble' doesn't really mean anything.

> I understand that in some case it might make some extra registers
> available, but at the same time the way handshaking is done also
> changes. So does that mean that hardware starts interpreting the
> lines in different way in different modes? Or does that mean that it
> crosses some lines through its internal logic so that correct lines
> affect corret registers?

The chipset mode just makes extra registers available to the software,
but has no effect on the peripheral.  From the peripheral's point of
view there is no difference -- any transfer mode can be used from any
chipset mode, it's just that some chipset modes make it easier (or
faster) for the software to perform the transfer.

Tim.
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