Common Options : EPP 1.7, EPP 1.9

Details

This feature is usually found under the Parallel Port Mode option. It's linked to that option so if you did not enable either the EPP or ECP+EPP mode, this feature will disappear from the screen or appear grayed out. This feature is used to select the version of EPP that the parallel port should use. There are two selectable versions - EPP 1.7 and EPP 1.9.

Generally, EPP 1.9 is the preferred setting because it supports the newer EPP 1.9 devices and most EPP 1.7 devices; and offers advantages like support for longer cables. However, because certain EPP 1.7 devices cannot work properly with an EPP 1.9 port, this BIOS feature has been implemented to allow you to set the EPP mode to EPP 1.7 when such an issue crops up.

For more information, check out KasperPedersen's explanation :-

In the EPP protocol, the port asserts a request strobe (I want to read/write). The attached device reads the data, and asserts an acknowledge strobe (I have taken/provided the data). The port then negates the strobe (operation done). Finally the attached device negates its acknowledgement (I'm ready for another operation).

The difference between 1.7 and 1.9 is the last state where the attached device removes the acknowledge strobe. 1.7 ports don't check that the device has negated the acknowledge strobe, but presumes that the device will have removed it when 125ns have passed. This can be a problem if cables are long.

This was fixed in 1.9: Before it starts a cycle, it waits for the attached device to negate the acknowledge strobe from the last cycle. This allows for a cleaner hardware design at the device end; and longer cables (50m possible if IEEE1284 is used, even though that's outside the specs.)

It sums down to that setting the port for 1.9 is compatible with previous 1.7 devices, but setting the port for 1.7 will cause problems with 1.9 devices or long cables. The reason it's an option at all is that "some" 1.7 devices won't cope with a new cycle less than 125 ns after the port has negated the request strobe. This is to be considered a hardware bug in the device.

Dekeonus provided this piece of information from Warp Nine Engineering - The IEEE 1284 Experts :-

The EPP protocol was originally developed by Intel, Xircom and Zenith Data Systems, now referred to as EPP1.7 (in reference to a Xircom proposal version 1.7) EPP1.9 (more correctly 1284 EPP) was the protocol that was adopted as one of the IEEE 1284 advanced modes.

The EPP1.7 mode is provided for backward compatibility as a 1284 EPP compatible peripheral will work properly with an EPP 1.7 version host adapter, but an EPP 1.7 peripheral may not operate properly with a 1284 compliant host.