What are the factors of consideration in designing computer bus

The factors of a bus design are explained below__

Bus Design

Bus types                                 Method of Arbitration

(i) Dedicated                                    (i) Centralized

(i) Multiplexed                                 (ii) Distributed

Timing                                    Bus width

(i) Synchronous                     (i) Address

(ii) Asynchronous                  (ii) Data

Data Transfer Type:

(i) Read

(ii) Write

(iii) Read- modify – write

(iv) Read- after write

(v) Block

Bus Types: Bus lines can be separated into two generic types__

          (i) Dedicated

          (ii) Multiplexed

A dedicated bus line is permanently assigned either to one function or to a physical subset of computer components.

Method of using the same liners for multiple purposes is known as time multiplexing.

Method of Arbitration: In all but the simplest systems, more than one module my need control of the bus. For example, an I/O module.

The methods of arbitration are __

          (i) Centralized

          (ii) Distributed

Centralized: In a centralized scheme, a single hardware device, referred to as a bus controller or arbiter is responsible for allocating time on the bus.

Distributed: In distributed scheme, there is no central controller; rather, each module contains access control logic and the modules act together to share the bus.

Timing: Timing refers to the way in which events are co-ordinate on the bus. Buses use either_

          (i) Synchronous timing.

          (ii) Asynchronous timing

Synchronous timing: With synchronous timing, the occurrence of events on the bus is determined by a clock.

Asynchronous timing: With asynchronous timing the occurrence of one event on a bus follows and depends on the occurrence of a previous event.

Bus width: We have already addressed the concept of bus width. The width of the data bus has an impact on system performance. The wider the data bus, the greater the number of bits transferred at one time.

Data transfer type: All buses support both write (master to slave) and read (slave to master) transfers. A read – modify-write operation is simply a read followed immediately by a right to the same address.

Read-after-write is an individual operation consisting of a right followed it immediately by a read from the same address.

Some bus system also suffered a block data transfer. In this case, one address cycle is followed by in data cycles.