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The first seven 1-bits of this (the pattern 01111111) constitute a "go-ahead" sequence (also called EOP, end of poll) giving a secondary permission to transmit. A secondary which wishes to transmit uses its 1-bit delay to convert the final 1 bit in this sequence to a 0 bit, making it a flag character, and then transmits its own frames.
The communication links, across which computers (or parts of computers) talk to one another, may be either serial or parallel. A parallel link transmits several streams of data simultaneously along multiple channels (e.g., wires, printed circuit tracks, or optical fibers); whereas, a serial link transmits only a single stream of data.
Synchronous serial communication describes a serial communication protocol in which "data is sent in a continuous stream at constant rate." [1]Synchronous communication requires that the clocks in the transmitting and receiving devices are synchronized – running at the same rate – so the receiver can sample the signal at the same time intervals used by the transmitter.
There are two ways to synchronize the two ends of the communication. The synchronous signalling methods use two different signals. A pulse on one signal indicates when another bit of information is ready on the other signal. The asynchronous signalling methods use only one signal.
It is sometimes called a four-wire serial bus to contrast with three-wire variants which are half duplex, and with the two-wire I²C and 1-Wire serial buses. Typical applications include interfacing microcontrollers with peripheral chips for Secure Digital cards, liquid crystal displays , analog-to-digital and digital-to-analog converters ...
A serial port is a serial communication interface through which information transfers in or out sequentially one bit at a time. [1] This is in contrast to a parallel port , which communicates multiple bits simultaneously in parallel .
Stop (logic high (1)): the next one or two bits are always in the mark (logic high, i.e., 1) condition and called the stop bit(s). They signal to the receiver that the character is complete. Since the start bit is logic low (0) and the stop bit is logic high (1) there are always at least two guaranteed signal changes between characters.
Modbus or MODBUS is a client/server data communications protocol in the application layer. [1] It was originally designed for use with programmable logic controllers (PLCs), [2] but has become a de facto standard communication protocol for communication between industrial electronic devices in a wide range of buses and networks.