Types of transfers supported by interconnection structure.

· Memory to CPU: The CPU reads an instruction or unit of data from memory.

· CPU to Memory:The CPU writes a unit of data to memory.

· I/O to CPU: The CPU reads data from I/O device via an I/O module.

· CPU to I/O: The CPU sends data to the I/O device.

· I/O to or from the Memory: For these two cases, an I/O module is allowed to exchange data directly with memory, without going through the CPU, using direct memory access (DMA).

Multiplexer is a functional device which permits to two or more channels of data link to use the same common device of data transfer jointly.

Bus Structure

A system bus consists, typically, of from 50 to 100 separate lines, which can be classified into three functional groups: data, address and control lines (power lines are usually omitted ).

z Control and timing information(indicate validity of data and address information) y Memory read/write signal y Interrupt request

Command signals specify operations to be performed. Typical control lines include:

q Memory Write: Causes data on the bus to be written into the addressed location.

q Memory Read: Causes data from the addressed location to be placed on the bus.

q I/O Write: Causes data on the bus to be output to the addressed I/O port.

q I/O Read: Causes data from the addressed I/O port to be placed on the bus.

q Transfer ACK: Indicates that data have been accepted from or placed on the bus.

q Bus Request: Indicates that a module needs to gain control of the bus.

q Bus Grant: Indicates that a requesting module has been granted control of the bus.

q Interrupt request: Indicates that interrupt is pending.

q Interrupt ACK: Acknowledges that the pending interrupt has been recognized.

q Clock: Used to synchronize operations.

q Reset: Initializes all modules.

The operation of any bus is as follows:

If one of the modules “wishes” to send data to another, it must do two things:

1. Obtain the use of the bus;

2. Transfer data through the bus.

If one of the modules “wishes” to receive data from the other module it must do:

1. Obtain the use of the bus;

2. Send request to the other module, by putting the corresponding code on the address lines after formation signals on the certain control lines.

Computer systems contain a number of different buses that provide pathways between components at various levels of the computer systems hierarchy.

Date: 2015-12-24; view: 3615

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