Data transfer schemes in Microprocessor :-
Data can be transferred between memory, microprocessor and input output devices. the speed and format of all the input output devices does not matches microprocessor.For example some input output devices like ABC' and DAC's are slow as compared to microprocessor.Some devices are serial in nature while microprocessor is parellal in nature.Because of this, number of data transfer schemes have been devided to cope with this problem.The data transfer schemes can be broadly clasified into two categories :-
Programmed Data Transfer
Direct Memory Access Data Transfer
Programmed Data Transfer:-
Programmed Data transfer schemes can be classified in four Categories:-
1.Programmed Data Transfer Scheme:-
In this scheme, data transfer takes place under the control of a program residing in the main memory of the microcomputer system. So microprocessor executes a program to perform all data transfers between the memory and i/o device via egister. This data transfer takes place under the control microprocessor.As the transfer of data takes place through a register, generally accumulator and requires execution of several instructions,so programmed data transfer is slow and suitable for small data.
It can be classified in four types :-
Synchronous Data Transfer:-
In this scheme, timing characteristics of I/O device are precisely known. Speed og I/O devices matches microprocessor always consider the I/O device to ready for data transfer.
Synchronous Data Transfer With Delay :-
In this scheme,of I/O device is slow as compare to microprocessor but timing characteristics are precisely known. Microprocessor initates I/o device to get ready and than waits for some predetermined than executes I/O instruction to complete the data transfer .
Asynchronous Data transfer :-
In this scheme data transfer between external device and microprocessor occurs via handseking process there is some exchange of signals between I/O and microprocessor before the actual data transfer takes place.
Interrupt Driven Data Transfer:-
In this scheme, microprocessor initates data transfer by requesting the device' to get ready' and than goes executin its main problem instead of wasting its time by continuesly checking the statues of input output device.Whenever device is ready to accept or supply data, it informs microprocessor through a special interrupt line.
Direct Memory Access :-
In this scheme data is transferred between memory and I/O device without any involvement of microprocessor. Microprocessor is sidelined in this process by tristating its addres bus,data bus and control bus. A direct link is establishment between memory and I/O device. Data transfer takes place under the control of an external circuit DMA controller. This technique is used to trnsfer blocks of data between memory and I/O devics.