Bus-based computer systems

Bus-based computer systems can be created by using good choice of microprocessors, input/output devices and appropriate memory components. CPU bus is a set up used for the interconnection of these constituent components. Thus through bus, CPU communicates with memory and input/output devices. A bus is a collection of wires and defined by a protocol. This protocol allows smooth communication between CPU and memory/input/output devices. Bus provides an effective and excellent interface to memory. The basic building block of bus protocol is four-cycle handshake. This block ensures that when two devices want to communicate, one is ready to transmit and the other is ready to receive. Here two wires are used for this purpose. These wires are named as ‘enq’ meaning enquiry and ‘ack’ meaning acknowledge. Some additional wires are also used during data transmission. In the first cycle, the first device raises its output to signal an enquiry. This makes second device ready for reception of data. In the second cycle, second device raises its output to signal acknowledgement. Now both the devices are ready for transmission and reception. In the third cycle, second device lowers its output and signals the complete reception of data. In the fourth and last cycle, first device lowers its output.

Flip-flop circuits

The present era, the era of digital devices mainly concerned about storage technology. Storage of data and processing of data are the two main functions that to be attended in digital technology. Binary counting devices require digital devices with two stable states. These devices are capable of undergoing a change from one state to another by the application of a trigger pulse to one of its inputs. A flip-flop is an ideal circuit with two stable states. It is capable of storing a signal like a ‘memory’ until new signal is applied to the circuit. Different types of flip-flops exist in the market. They are Set-Reset (SR) flip-flop, JK master slave flip-flop and D-flip-flop. SR flip-flops have two inputs and two outputs. Either NOR gates or NAND gates are used for the construction of SR flip-flop. An emitter-coupled bistable multivibrator can be used as an SR flip-flop. Master slave principle is used in JK master slave flip-flops. The main application of JK master slave flip-flops are in complex counters. Only one input is provided in D-flip-flops and they are widely used in shift registers and sequential logic circuits.