The Universal Asynchronous Receiver/Transmitter, commonly referred to as the UART, is an asynchronous transceiver that is part of the computer hardware. It converts the data to be transferred between serial communication and parallel communication. As a chip that converts parallel input signals into serial output signals, the UART is typically integrated into the connections of other communication interfaces. The actual physical representation is a stand-alone modular chip or as a peripheral device integrated in the microprocessor. It is generally RS-232C-compliant and is paired with a standard signal amplitude conversion chip such as Maxim's MAX232 as an interface to external devices.
At present, the UART (Universal Asynchronous Receiver Transmitter) interface is used more and more widely, and a UART interface is provided on many devices. Industrial use microprocessors generally only include 2 UART ports. In the actual industrial data transmission and acquisition application system, in order to save resources, the microprocessor directly interacts with the device through the UART port.
This will inevitably lead to insufficient UART port of the microprocessor. In order to facilitate the access of the device, extending the UART port is an ideal solution. At the same time, considering that the microprocessor can connect multiple bus devices on the SPI/I2C bus, in order to make full use of resources, the UART interface can be extended by SPI/I2C in practical applications.
This paper proposes a method of SPI expansion UART, mainly using SC16IS752 chip for UART interface expansion. The SC16IS752 provides a standard SPI bus interface that requires only a standard SPI or analog SPI bus interface. The entire design is simple, economical and versatile.
Finally, the application of the extended interface in the wireless data collection concentrator is introduced. It is convenient to use the extended UART port to connect the corresponding wireless communication module to realize data collection and communication.
SPI busThe Serial Peripheral Interface (SPI) is a synchronous serial interface introduced by Motorola. Its hardware is powerful, so the software related to SPI is relatively simple [2]. In general, three to four lines are required to implement SPI communication: the synchronous clock (SCK) line, which is used to synchronize the serial data transmission between the master and slave devices on the MISO and MOSI lines; the main output/slave input (MOSI) Line, for the output of the master device or the input of the slave device; the master input/slave output (MISO) line for the input of the master device or the output of the slave device; the chip select control (CS) line for the selection of the slave device . There are four working modes of SPI, and this paper adopts one of the main modes.
SC16IS752 expansion chipThe SC16IS752 is a chip that has been extended by NXP to the UART interface via the SPI/I2C bus [3]. Expands the dual-channel high-performance UART and reaches a data rate of 5Mbps; provides eight additional programmable I/O pins; and provides IrDA with data rates up to 115.2kbps. In addition, SC16IS752 has other advanced features, such as automatic hardware and software flow control, automatic RS485 support and software reset as UART expansion interface chip. The pin definition of SC16IS752 is not complicated, as shown in Figure 1.
XTAL1, XTAL2 pin is used to connect the crystal oscillator circuit, CS/A0 is used as SPI chip select or I2C bus device address selection A0; I2C/SPI is I2C bus or SPI bus interface selection; IRQ interrupt pin. The other pins mainly include the extended 2 UARTs and I/O. The connection of the microprocessor with SPI interface to the SC16IS752 is very convenient; if the SPI interface is not available, the function of the analog SPI port can be realized through the I/O port.
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