The Universal Asynchronous Receiver/Transmitter, commonly known as UART, is a key component in computer hardware that facilitates asynchronous data communication. It acts as a bridge between serial and parallel data formats, converting parallel input signals into serial output signals. Typically, the UART is integrated into other communication interfaces, either as a standalone chip or as a peripheral within a microprocessor. Most UARTs are RS-232C compliant and often work with signal level conversion chips like the MAX232 from Maxim to interface with external devices.
Today, UART interfaces are widely used across various devices, especially in industrial applications where microprocessors usually have only two built-in UART ports. To optimize resource usage, these microprocessors often communicate directly with peripherals through the UART port. However, this can quickly lead to a shortage of available UART ports, especially in complex systems requiring multiple connections.
To address this limitation, expanding the UART interface becomes an efficient solution. One practical approach is to use the SPI or I2C bus, which many microprocessors already support, to extend the number of available UART ports. This not only maximizes resource utilization but also simplifies system design.
This paper introduces a method for expanding the UART interface using the SPI bus, specifically utilizing the SC16IS752 chip. The SC16IS752 offers a standard SPI interface and supports high-speed data transfer up to 5 Mbps. It provides two enhanced UART channels, eight programmable I/O pins, and IrDA support at 115.2 kbps. Additional features include automatic flow control, RS485 support, and a software reset function, making it ideal for UART expansion.
The SC16IS752 is designed with a straightforward pinout, allowing easy integration with microcontrollers that have an SPI interface. If an SPI interface is unavailable, the chip can still be controlled via an analog SPI implementation using general-purpose I/O pins. This flexibility makes it a popular choice in embedded systems.
Finally, this paper demonstrates how the extended UART interface can be applied in a wireless data collection concentrator. By connecting a wireless communication module to the expanded UART port, the system can efficiently collect and transmit data, enhancing its functionality and scalability.
**SPI Bus**
The Serial Peripheral Interface (SPI) is a synchronous communication protocol developed by Motorola. It is known for its robust hardware capabilities, which make the associated software relatively simple. SPI typically requires four signal lines: SCK (clock), MOSI (master out, slave in), MISO (master in, slave out), and CS (chip select). These lines enable reliable data exchange between a master device and one or more slave devices. There are four operating modes, and this paper uses one of the primary modes for communication.
**SC16IS752 Expansion Chip**
The SC16IS752 is a highly versatile UART expansion chip from NXP, capable of extending UART functionality over an SPI or I2C bus. It supports two high-performance UART channels, operates at speeds up to 5 Mbps, and includes eight programmable I/O pins. Additionally, it supports IrDA communication at 115.2 kbps and offers advanced features such as hardware and software flow control, automatic RS485 support, and a software reset function. Its pin configuration is straightforward, making it easy to integrate into a wide range of systems.
The SC16IS752 has several important pins, including XTAL1 and XTAL2 for the crystal oscillator, CS/A0 for chip selection or I2C address setting, I2C/SPI for interface mode selection, and IRQ for interrupt signaling. Other pins are dedicated to the two extended UARTs and the additional I/O lines. Connecting the microcontroller with an SPI interface to the SC16IS752 is simple and efficient. Even if an SPI interface is not available, the chip can still be operated using an analog SPI setup through the I/O pins. This adaptability makes the SC16IS752 a powerful tool for expanding UART capabilities in embedded systems.
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