Question

a. Discuss the merits and demerits of using a single bus.

b. How will the use of a mezzanine bus architecture solve this problem?

c. Discuss various methods of bus arbitration.

Answer 1

a. Discuss the merits and demerits of using a single bus.
Answer:-------
Merits:

• Low cost
• Simple to operate

Demerits:

• Difficult to do maintenance operations
• Failure of bus results in failure of the whole substation
• Can only be employed where loads can be interrupted or where we have some other supply source

b. How will the use of a mezzanine bus architecture solve this problem?
Answer:-------

This traditional bus architecture is reasonably efficient but begins to break down as higher and higher performance is seen in the I/O devices.

In response to these growing demands, a common approach taken by industry is to build a high speed bus that is closely integrated with the rest of the system, requiring only a bridge between the processor’s bus and the high-speed bus. This arrangement is sometimes known as a mezzanine architecture.

c. Discuss various methods of bus arbitration.
Answer:-------
Bus arbitration is the process by which the next device to become the bus master is selected and bus mastership is transferred to it. The selection of bus master is usually done on the priority basis.

There are two approaches to bus arbitration: Centralized and distributed.
1. Centralized Arbitration
In centralized bus arbitration, a single bus arbiter performs the required arbitration. The bus arbiter may be the processor or a separate controller connected to the bus.
There are three different arbitration schemes that use the centralized bus arbitration approach. There schemes are:

• Daisy chaining
• Polling method
• Independent request

2. Distributed Arbitration

• In distributed arbitration, all devices participate in the selection of the next bus master.
• In this scheme each device on the bus is assigned a 4-bit identification number.
• The number of devices connected on the bus when one or more devices request for the control of bus, they assert the start-arbitration signal and place their 4-bit ID numbers on arbitration lines, ARB0 through ARB3.
• These four arbitration lines are all open-collector. Therefore, more than one device can place their 4-bit ID number to indicate that they need to control of bus. If one device puts 1 on the bus line and another device puts 0 on the same bus line, the bus line status will be 0. Device reads the status of all lines through inverters buffers so device reads bus status 0as logic 1. Scheme the device having highest ID number has highest priority.
• When two or more devices place their ID number on bus lines then it is necessary to identify the highest ID number on bus lines then it is necessary to identify the highest ID number from the status of bus line. Consider that two devices A and B, having ID number 1 and 6, respectively are requesting the use of the bus.