Editing Parallel port (section)

===EPP and ECP===
The introduction of new devices like [[Image scanner|scanner]]s and [[multi-function printer]]s demanded much more performance than either the Bi-Tronics or IBM style backchannels could handle. Two other standards have become more popular for these purposes. The Enhanced Parallel Port (EPP), originally defined by [[Zenith Electronics]], is similar to IBM's byte mode in concept, but changes details of the handshaking to allow up to 2 MB/s.<ref>{{patent|EP|0640229|Buxton, C.L. / Kohtz, R.A. / Zenith Data Systems Corp.: ''Enhanced parallel port.'' filing date 15 May 1992}}</ref> The Extended Capability Port (ECP) is essentially an entirely new port in the same physical housing that also adds [[direct memory access]] based on [[Industry Standard Architecture|ISA]] and [[run-length encoding]] to compress the data, which is especially useful when transferring simple images like [[fax]]es or black-and-white scanned images. ECP offers performance up to 2.5 MB/s in both directions.<ref name=lava>{{cite tech report |url=http://www.nor-tech.com/solutions/dox/ieee1284_parallel_ports.pdf |title=IEEE 1284: Parallel Ports |publisher=Lava |date=2002 |access-date=2 November 2007 |archive-url=https://web.archive.org/web/20060523125620/http://www.nor-tech.com/solutions/dox/ieee1284_parallel_ports.pdf |archive-date=23 May 2006 |url-status=dead |df=dmy-all }}</ref>

All of these enhancements are collected as part of the [[IEEE 1284]] standard. The first release in 1994 included original Centronics mode ("compatibility mode"), nibble and byte modes, as well as a change to the handshaking that was already widely used; the original Centronics implementation called for the BUSY lead to toggle with each change on any line of data (busy-by-line), whereas IEEE 1284 calls for BUSY to toggle with each received character (busy-by-character). This reduces the number of BUSY toggles and the resulting interruptions on both sides. A 1997 update standardized the printer status codes. In 2000, the EPP and ECP modes were moved into the standard, as well as several connector and cable styles, and a method for [[Daisy chain (electrical engineering)|daisy chaining]] up to eight devices from a single port.<ref name=lava/>

Some host systems or print servers may use a strobe signal with a relatively low voltage output or a fast toggle.  Any of these issues might cause no or intermittent printing, missing or repeated characters or garbage printing. Some printer models may have a switch or setting to set busy by character; others may require a handshake adapter.{{citation needed|date=October 2016}}