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There are many different protocols, such as Centronics, EPP, ECP, LapLink, Dongles, and so forth, for reading from and writing to devices on the parallel port. The Windows NT 3.1, 3.5, and 3.51 parallel drivers implement the Centronics protocol for writing to printers. The parallel drivers for Windows NT 3.5 also add the ability for many parallel device drivers to share the parallel port. So, while Windows NT 3.5 and 3.51 does not directly support every parallel protocol, it does make it much easier to add these protocols to the system. For example, suppose that you want to add bidirectional capabilities. If you have a device on the parallel port that understands the Centronics protocol for writing to the device, and understands some other parallel protocol for reading from the device, then you can write a separate parallel class driver to implement READ. Then, an application can direct its WRITE requests to the normal parallel driver and its READ requests to the new specialized parallel driver. The contention between these two drivers would be resolved by the parallel port contention support provided by the Windows NT parallel port driver. As another example, you can add a dongle parallel class driver, which would allow applications to write to the printer and read from the dongle on the same parallel port. Future releases of Windows NT will implement other important parallel protocols using the parallel port contention support released in Windows NT versions 3.5 and 3.51. Additional query words: 3.10 3.50
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