Test: Programmable Communication Interface 8251 USART - Computer Science Engineering (CSE) MCQ

Basically, there are three modes of data transmission. simplex, duplex and half duplex.

 In simplex mode, the data transmission is unidirectional. For example, a CPU may transmit data for a CRT display unit in this mode.

 In half duplex mode, data transmission is bidirectional but not at a time. For example, Walkie-Talkie.

Transmitter Clock Input (TXC(active low)) is a pin that controls the rate at which the character is to be transmitted.

Transmitted Data Output pin carries serial stream of the transmitted data bits along with other information like start bits, stop bits and parity bits etc.

 RXRDY(Receiver ready output) may be used either to interrupt the CPU or polled by the CPU.

RS232C has been used for long and has a few disadvantages like limited speed of communication, high-voltage level signaling and big-size communication adapters.

The USB standards support the signaling rates. Also, USB signaling is implemented in differential in low- and full-speed options.

The token packet is a second type of packet which commands the device either to receive data or transmit data.

PRE packets are only of importance to low-speed USB devices.