Parallel data is transmitted eight bits at a time. The standard covering port technologies (IEEE 1284), and that parallel ports are used primarily for printers. |
There isn't as much to know about parallel ports as there is to know about serial ports. Parallel data moves around much faster than serial data, which is why the internal bus structures of the PC use a parallel format. Parallel ports were originally designed specifically for printers,. However, other devices have been adapted to them, including other types of output devices, input devices, all taking advantage of the bidirectional capabilities of IEEE 1284 parallel devices. These include some external CD-ROMs, external tape drives and Zip drives, as well as file transfer software over proprietary cabling. Parallel cables should not be more than 15 feet in length. |
In 1984, parallel port protocols were standardized by the IEEE (Institute of Electrical and Electronics Engineers). The standard, formerly titled "IEEE Standard Signaling Method for Bidirectional Parallel Peripheral Interface for Personal Computers," or IEEE 1284 as it is commonly known, incorporates the two parallel port standards that had been used to that point with a new protocol, creating an all-encompassing port model. The standards included in IEEE 1284 are as follows. |
Standard Parallel Port (SPP) allows data to travel one-way only ---- from the computer to the printer. |
Enhanced Parallel Port (EPP) allows data to flow in both directions, but only in one direction at a time. This lets the printer communicate to the processor or adapter to signal it is out of paper, its cover is open, and so on. |
Enhanced Capablities Port (ECP) allows bidirectional communications over a special cable, one that is IEEE 1284 compliant. Many bi-directional cables exist, but they may be EPP cables, which do not support ECP communications. |
** IEEE 1284 established the standard for bi-directional communications on the parallel port, and the ECP protocol allows for full-duplex (simultaneous communications in two directions) parallel comunications.** |