Universal Receiver-Transmitters

Figure 7-17.—Independent request control. Procedural —The.procedural characteristics define how signals are to be exchanged and the environment necessary to input and output data. No matter the format, I/O interfacing components are generally used by most computers regardless of the computer type. I/O INTERFACING COMPONENTS The computer’s I/O processor, regardless of the type of computer and regardless of the type of format (serial or parallel) must ensure that the voltage levels between the computer and the external equipments are compatible. The primary circuitry that accomplishes this is located on an I/O pcb or modules/pcb’s that make up an IOA. Some of the primary I/O interfacing hardware includes universal receiver transmitters, line drivers, and line receivers. Universal Receiver-Transmitters Within a digital computer, the data is transferred internally using a parallel format. All the bits of a byte or memory word are exchanged simultaneously between registers, buses, and other computer logic. For the data to be communicated over a serial channel, it must be converted from parallel to a serial bit stream. Universal receiver-transmitters come in three types: universal asynchronous receiver- transmitters (UARTs), universal synchronous receiver- transmitters (USRTs), and universal synchronous/ asynchronous receiver-transmitters (US ARTS). A UART, USRT, or USART may be built into the computer or added as part of an I/O pcb or serial interface board. Modern UARTs, USRTs, or USARTs may consist of a single IC chip. We take a look at a USART as an example of this type of logic assembly. The USART is designed to function as a peripheral device to the microprocessor. The microprocessor transmits byte-oriented data (data and command/control words) to the US ART and receives byte-oriented data (data and status words) from the USART. The actual conversion from serial to parallel or parallel to serial is performed by the USART and is transparent to the microprocessor. The standard 7-19