Design of logistics PDA wireless terminal based on S3C44BOX processor and Linux operating system

The advancement of science and technology has brought about tremendous changes in the logistics industry, from mechanization to automation and intelligence. my country's logistics industry started late and is still under manual management or semi-automatic management, with low efficiency. With the development of the logistics industry, the scale of warehousing continues to expand, and the types of goods continue to increase, which has brought about a series of chain reactions, causing the traditional logistics industry to become increasingly difficult.

The development of embedded extension technology can provide powerful and flexible solutions for the field of logistics MA control. The research plan of this article applies the embedded expansion technology system to the field of logistics control, using embedded processors and rich peripheral expansion interfaces, coupled with LCD touch screens, to achieve human-computer interaction. Combined with the barcode collector, it can collect data information in real time and connect to the server database in real time through wireless transmission; real-time inventory of goods, incoming and outgoing warehouses; real-time information query and timely dispatch; it also has the ability to store voice data, simple and fast, avoid human errors, streamline manpower, and manage inventory. , shorten complicated procedures, save time, improve service quality and other characteristics.

1 System hardware design

1.1 Hardware system composition

The target hardware platform is mainly divided into three parts: processor core, peripheral circuits in the chip, and board-level peripheral circuits. This system mainly includes ARM processor, memory, barcode scanner, wireless transceiver chip, LCD display and touch screen. Its structure diagram is shown in Figure 1.

1.2 Main hardware selection and circuit design

1.2.1 Embedded processor

This system uses Samsung's S3C44BOX processor, which is a cost-effective microprocessor specially provided for handheld devices and general applications. It uses the ARM7TDMI core and works at 66 MHz. This chip contains very rich on-chip resources. Almost all commonly used chip-level bus structures have corresponding hardware controllers, and peripheral expansion is very convenient.

1.2.2 External memory

In order to meet the application needs of logistics PDA, this system uses Flash, SDRAM, and NAND Flash memory.

The main feature of Flash Memory is to save information when power is turned off. It has the characteristics of ROM, high access speed, easy erasing and rewriting, and low power consumption. It is usually used in the system to store operating system and program code, as well as some user data that needs to be saved after the system is powered off. After the system is powered on or reset, the first instruction is obtained and execution begins. This system uses a 16-bit AM29LV160B linear Flash memory with a single-chip storage capacity of 2 MB. Flash and S3C44BOX are connected to the chip select terminal nGCS0 through a resistor, and an external pull-up resistor is connected; the data line and the address line are connected respectively; the read and write terminals are connected to nOE and nWE respectively.

SDRAM has the characteristics of large storage capacity, low price, and will not be saved when power is turned off. In this system, it is mainly used to store running programs and data stacks. This system uses Hyundai's 57V series HY57V641620, which is a 4 Banks × 1 M × 16 bit SDRAM chip. The single-chip storage capacity is 4 banks × 16 M^i (8 MB). In order to meet the needs of the complex logistics data information system and give full play to the data processing capabilities of the 32-bit CPU, the system uses two 8 ns HY57V641620 in parallel to form a 32-bit SDRAM memory system. Through nSCS strobe, nSRAS and nSCAS are used to strobe row address and column address addressing respectively.

NAND Flash is cheap, has large storage capacity, is cost-effective, is very lightweight, and has good shock resistance, making it suitable for digital products. This article uses the K9F2808U0B 16 M×8-bit memory chip with a voltage range of 2.7 V to 3.6 V. When the USB control chip is in SLAVE mode, files can be downloaded from the PC and stored in NAND Flash. When the inventory taker takes the PDA to take inventory, the system can directly call the stored data file. When the inventory taker completes the count, a copy of the data can also be retained in the NAND Flash for query at any time, and the voice data can also be saved. The NAND Flash is gated through GPC15, and the corresponding nOE and nWE perform read and write operations. The connection circuit diagram of each memory and processor is shown in Figure 2.

1.2.3 LCD liquid crystal display and touch screen module

The ARM processor S3C44BOX includes an LCD controller that supports grayscale LCD and color LCD. This design uses two 74HC245 decoders to control the LCD pixel output and control signals respectively. This article uses the TFT color 3.9-inch display LQ039Q2DS54 with a resolution of 320×240 and the ADS7843 touch screen driver chip. S3C44BOX simulates the serial SIO interface through the port PG and transmits data with the touch screen control chip ADS7843 to complete the reading of the touch position coordinates of the touch screen. ADS7843 mainly completes the switching of electrode voltage, acquisition of voltage value at the contact point and A/D conversion. The interface circuit diagram is shown in Figure 3.

1.2.4 Interface design

(1) RS232 interface design

Since S3C44BOX only has 2 channels of UART and does not integrate an RS-232C interface, MAX202 is selected as the level conversion chip from UART to RS-232C so that it can communicate serially with other devices such as PCs and obtain data and voice information, which is convenient update data. Choose a 9-pin DB9 header and use 3 lines: GND, RXD, and TXD.

(2) JTAG interface

Because the JTAG signal is integrated in the S3C44BOX, the device can be debugged by simply pulling out the signal line.

(3) Audio interface design

In order to store voice information, the UDA1314 chip of Philips Company is selected to complete the analog-to-digital conversion of the sound signal. The chip integrates a stereo analog-to-digital converter and a digital-to-analog converter on a single chip. The analog-to-digital conversion part of the chip includes a programmable gain amplifier and a digital automatic gain controller, and uses bit stream conversion technology for signal processing. In view of its low power consumption and low voltage characteristics, UDA1341TS is very suitable for portable devices such as PDAs.

(4) USB interface design

The USB interface is a new generation standard interface bus with low cost, small space occupation, unified interface specifications, fast, two-way sharing, and plug-and-play. It is widely used in embedded system equipment. The CH372 chip used in this article is a universal device interface device for the USB bus. The local end has an 8-bit data bus and read, write, chip select control lines and interrupt outputs, which can be easily connected to the system bus of the microcontroller. In the computer system, the supporting software of CH372 provides a simple and easy-to-use operation interface. Communication with the local microcontroller is like reading and writing files. CH372 has built-in underlying protocols in USB communication, and has a trouble-free built-in firmware mode and a flexible external firmware mode. In the built-in firmware mode, CH372 automatically handles all transactions of the default endpoint O, and the local end is only responsible for data exchange, so the program is very simple. In the external firmware mode, the external microcontroller handles various USB requests as needed, so that devices that comply with various USB class specifications can be implemented.

By combining the USB interface with a mini barcode scanner with a USB interface, you can easily connect to a PDA to collect data on logistics goods. Make logistics data collection easy and fast. The interface design circuit diagram is shown in Figure 4.

1.2.5 Wireless communication module design

Choose a wireless transceiver module with 2.4 GHz wireless transceiver nRF2401 and enhanced 8051 core launched by NORDIC. nRF24E1 has small size and low power consumption. It is a highly integrated chip integrating wireless transceiver, 8051, ADC and other peripheral devices. It contains 125 frequency points and can realize point-to-point and point-to-multipoint wireless communication. At the same time, frequency changing and frequency hopping can be used to avoid interference. The maximum transmission rate of nRF24E1 can reach 1 M/s, and its maximum transmit power is 0 dBm. In an ideal environment, its indoor transmission distance can reach 30 m to 40 m, and its outdoor transmission distance can reach 100 m to 200 m. The circuit diagram is shown in 5.

The data obtained from the barcode scanner is transmitted to the nRF2401 through the processor, and then wirelessly sent to the AP (wireless access point), and then transmitted to the background computer database through the AP, so that the on-site and background data can be correlated to obtain correct real-time data. Efficiently and easily implement statistical inquiry of logistics inventory, entry and exit, and supply information.

2 Software design

The core of the operating system of the lower computer is the S3C44BOX operating system, which uses the Linux kernel to initialize the hardware through the Bootloader, boot the kernel and file system to start the Linux system. The software design is as follows:

(1) Bootloader design and implementation. Bootloader is the first piece of code executed before entering the operating system after the processor is reset, loading and booting to start the entire system. It is divided into two stages. Stage one is mainly about the processing and initialization work closely related to the CPU core and memory. This part is mainly in Flash. Phase 2 mainly implements support for general processes and peripheral extensions, which can streamline unnecessary drivers and reduce kernel running space.