What Is Parallel Communication?

Parallel means that multi-bit data is transmitted through parallel lines at the same time, so that the data transmission speed is greatly improved, but the length of the parallel transmission line is limited. As the length increases, interference will increase, and the data will be prone to errors.

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Parallel communication parallel interface

Generally, the parallel interface has three functions:

Realize the connection with the system bus: provide data input and output functions.

Achieve connection with peripherals: ensure effective data reception and transmission with peripherals.

(3) It has the function of interrupt request processing: the input and output of peripheral devices are implemented by interrupts.

Parallel communication interface connection

Typical bidirectional parallel interface to peripherals

Parallel interface and CPU connection

Data bus: It is a channel for data exchange between CPU and parallel interface.

Read and write signal lines: control the data flow and determine whether the operation is read or write.

(3) Reset line, ready status line: parallel interface data is ready.

Interrupt request line: The parallel interface makes an interrupt request to the CPU.

Address decoding circuit: choose different interface circuits, choose different registers inside the interface circuit.

Parallel interface and peripheral connection

Input device: data input line, device data ready status line and interface receive data response line.

Output device: data output line, interface data ready status line and peripheral device receive data answer line.

Parallel interface

Control register: Receive control command from CPU.

Data input buffer and data output buffer: input and output data.

(3) Status register: Provides the working status of the interface circuit for the CPU to query.

Parallel communication transmission principle

The process of inputting data to the parallel interface

The peripheral sends data to the "data input line", and the parallel interface is notified to take it through the "input data ready" status line. The interface latches the data to the "input buffer" and notifies the peripheral through the "data input response" line. The interface data buffer is full. Do not send any more data. The corresponding bit in the "Status Register" of the interface is set to 1. It is convenient for the CPU to query and the interface to send interrupt requests to the CPU.

After the CPU removes data from the interface, the interface clears the "data input ready" and "data input response" signals so that the peripheral can input the next data.

Process of parallel interface output data

The interface "data output buffer" is empty, and the "data output is ready" status line sends 1, receives the data sent by the CPU, resets it to 0, the data is sent to the peripheral through the "data output" line, and the "data output ready" The "" line tells the peripheral to fetch data.