One of the main purposes of a bus system is to allow the exc

One of the main purposes of a bus system is to allow the exchange of information and/or data between different devices. Describe an activity that you engage in that involves features similar to those of a synchronous bus system and one that involves features similar to those of an asynchronous bus system. Explain in each case how the advantages and features of the bus system apply to the activities that you listed.

Solution

A bus is a shared communication link, which uses one set of wires to connect multiple subsystems. The two major advantages of the bus organization are versatility and low cost.

A bus generally contains a set of control lines and a set of data lines. The control lines are used to signal requests and acknowledgments, and to indicate what type of information is on the data lines. The control lines are used to indicate what the bus contains and to implement the bus protocol. The data lines of the bus carry information between the source and the destination. This information may consist of data, complex commands, or addresses. Buses are tradi i ll l ifi d ditionally classified as processor-memory buses or I/O buses or special purposed buses (Graphics, etc. ). Processor memory buses are short, generally high speed, and matched to the memory system so as to maximize memoryprocessor bandwidth. I/O buses, b t t b l th h by contrast, can be lengthy, can have many types of devices connected to them, and often have a wide range in the data bandwidth of the devices connected to them. I/O buses do not typically interface directly to the memory but use either a processor-memory or a backplane bus to connect to memory. The major disadvantage of a bus is that it creates a communication bottleneck possibly limiting the maximum I/O communication bottleneck, possibly limiting the maximum I/O throughput. When I/O must pass through a single bus the When I/O must pass through a single bus, the bandwidth of that bus limits the maximum I/O throughput. R h b d i i diffi lt Reason why bus design is so difficult : - the maximum bus speed is largely limited by physical factors: the length of the bus and the number of devices. These physical limits prevent us from running the bus arbitrarily fast. - In addition, the need to support a range of devices with widely varying latencies and data transfer rates also makes bus design challenging. - it becomes difficult to run many parallel wires at high speed due to clock skew and reflection. The two basic schemes for communication on the bus are synchronous and asynchronous. If a bus is synchronous (e.g. Processor-memory), it includes a clock in the control lines and a fixed protocol for communicatin g that is relative to the clock. This type of protocol can be implemented easily in a small finite state machine. Because the protocol is predetermined and involves little logic, the bus can run very fast and the interface logic will be small. Synchronous buses have two major disadvantages: - First, every device on the bus must run at the same clock rate. - Second, because of clock skew problems, synchronous buses cannot be long if they are fast. A h b A n async hronous bus i t l k d It d t is not cloc k e d. It can accommo d a t e a wide variety of devices, and the bus can be lengthened without worrying about clock skew or synchronization problems.