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CS401 Computer Architecture and Assembly Language GDB Fall 2012

Do you agree with the statement that Parallel port is a bidirectional port? Argue your answer with detail reason.

Solution:

yes, i agree with the statement that Parallel port is a bidirectional port.
The original specification for parallel ports was unidirectional, meaning that data only traveled in one direction for each pin. With the introduction of the PS/2 in 1987, IBM offered a new bidirectional parallel port design. This mode is commonly known as Standard Parallel Port (SPP) and has completely replaced the original design.
Bidirectional communication allows each device to receive data as well as transmit it. Many devices use the eight pins (2 through 9) originally designated for data. Using the same eight pins limits communication to half-duplex, meaning that information can only travel in one direction at a time. But pins 18 through 25, originally just used as grounds, can be used as data pins also. This allows for full-duplex (both directions at the same time) communication.

Parallel ports are the bidirectional ports because the parallel port is extensively used in PCs, usually to communicate with close devices. This is due to the need of using many cables, at least 9 for software handshaking, but is common the use of more of them. The advantage of this port over the other extensively used PC port, the serial port, is its higher speed, about 10 times faster, and so in principle one can achieve data speeds in the order of several hundreds kilobytes per second. The most common connection using the PC parallel port is done with the printer. As long as the printer does not generate data, it only accept them, However there was no real need for that in the hardware, in fact there are several documents on the Web about how to make a unidirectional parallel port to be bidirectional. Today parallel ports are made bidirectional because some devices can take advance of it, like the Zip units.


A parallel port is a type of interface found on computers (personal and otherwise) for connecting peripherals. In computing, a parallel port is a parallel communication physical interface. It is also known as a printer port or Centronics port. It was a de facto industry standard for many years, and was finally standardized as IEEE 1284 in the late 1990s, which defined a bi-directional version of the port. Today, the parallel port interface is seeing decreasing use because of the rise of Universal Serial Bus (USB) and FireWire (IEEE 1394) devices, along with network printing using Ethernet.
The parallel port interface was originally known as the LPT port (Line Print Terminal or Local Print Terminal) on IBM PC-compatible computers. According to the Jargon File, a similar port naming convention was used on ITS, DEC systems, and CP/M. It was designed to operate a text printer that used IBM’s 8-bit extended ASCII character set. The name derives from the fact that “line printer” was a common generic term at the time for any type of text printer. Graphical printers, along with a host of other devices, have been designed to communicate with the system.

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