what is parallel port?
A connector for a device that send and recieve several bits of data simultaneously.
three modes for parallel communication:-
1)compatible mode 2)nibble mode 3)byte mode
1) personal computers today are equipped with a parallel port Because the parallel port is a perfect choice for connection to other peripheral devices.
to transfer data parallely.
2) communication to parallel ports limited beacause it is unidirectional and no standard for interface.
3) In 1994,the new parallelport standard devloped by IEEE is 1284 standard.
4) this standard based on centronic standard parallel port(SPP).
5)standard parallel port is known as centronic paralel port.
6) in centronic mode ,it is unidirectional which means from host to peripherals.for example—printer.
7)1284 standard compatible with EPP and ECP.
8) 1284 standard provide improved performance while retaining backward compatibility.
9)In nibble and byte mode data can be transfered in reverse direction.
>why there is a need of communication in reverse dirction?
As the technology grows its strands with time ,we have scanner from which we scan the documents.
For bidirectional communication ,firstly,we have option at boot time and second by setting control register 5th bit set for input and zero for output.
what is handshaking?
i) reciever busy’s output tells the sender when it’s ready to recieve data.
ii)sender’s strobe output tells the reciever that a byte is available to read on data lines.
iii)reciever read data and sends acknowledgement that byte is recieved.
