RS232 Communication Questions and Answers for Viva - 232

Answer-1: RS-232 (ANSI/EIA-232 Standard) is the serial connection historically found on IBM-compatible PCs. It is used for many purposes, such as connecting a mouse, printer, or modem, as well as industrial instrumentation.

Answer-2: Valid RS-232 signals are either in the range of +3 V to +15 V or the range -3 V to -15 V with respect to the common ground (Figure 1-1). To be more specific, the driver output is Logic 0 when the voltage is between +5 V and +15 V and is Logic 1 when the voltage is between -5 V to -15 V. Received signal voltage level is that Logic 0 works on the received signal voltages up to +3 V to +15 V and Logic 1 works with voltages up to -3 V to -15 V.

Answer-3: For a quick estimate is to convert the capacitive load into the equivalent resistance. Before the driver is running out of juice, the power vs. load relation is pretty linear excluding the static power.

Answer-4: The charge pump needs to work with external flying capacitor and storage capacitor to generate the required voltage from the supply. Since the charge pump can double the supply voltage theoretically, it is recommended that the external capacitors have at least 10V working voltage.

Answer-5: Baud rate is a speed measurement for communication. It indicates the number of bit transfers per second.

Answer-6: Data bits are a measurement of the actual data bits in a transmission. When the computer sends a packet of information, the amount of actual data may not be a full 8 bits. Standard values for the data packets are 5, 7, and 8 bits. Which setting you choose depends on what information you are transferring.

Answer-7: Handshaking is a way of flow control of the communication in many RS-232 applications, which can be implemented in software or hardware. The main purpose of handshaking is to guarantee successful communication by preventing receiver from overloading. Receivers will let the transmitter device to hold data transmission if they are overloaded.

Answer-8: Parity is a simple form of error checking that is used in serial communication. There are four types of parity: even, odd, marked, and spaced.

Answer-9: Stop bits are used to signal the end of communication for a single packet. Typical values are 1, 1.5, and 2 bits.

Answer-10: In modern RS-232 transceivers, only one supply is needed to generate the valid RS-232 signaling. To generate the voltage level higher than the supply, it is common that charge pumps are employed in RS-232 ICs.

Answer-11: In RS-232 standard, the data rate is specified with the slew rate. Slew rate is defined as the change of an edge represented by difference in Voltage /difference in time, while rise time only counts the time of a transition (10% to 90%, or 20% to 80%).