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With the rapid development of computer technology, microelectronics technology, and network technology, embedded systems have been widely used in various fields such as agriculture and industry. This article mainly introduces the hardware design of ARM embedded systems and application examples of ARM embedded systems. Let’s follow the editor to learn more.
ARM Embedded System Hardware Design
Figure 1 is the system hardware structure diagram. The system uses an external 3.6864MHz crystal oscillator to generate the required clock of 18.432MHz, 36.864MHz, 49.152MHz, or 73.728MHz for the core.
The following mainly introduces the structure, memory expansion, main interfaces, display, and peripheral design of this hardware development platform.
1. Power Supply Design
The power supply is the guarantee of the reliable operation of the system, including the power supply and reset circuit parts. The system reset module provides the CS89712 startup signal. The system uses the nPOR signal as the reset signal, using a reset chip to generate the reset signal. As shown in Figure 2:
The external power input of the entire system uses DC 18V-36V, and the power supply of the system is relatively complex, with multiple voltage levels, among which the CS89712 chip I/O and core use 3.3V and 2.5V power supply respectively, while the expanded MAX125 and LCD display use 5V power supply. At the same time, the LCD contrast adjustment requires negative voltage bias (using MAX686 chip); the operational amplifier power supply voltage for the filtering and voltage following circuit in the analog acquisition MAX125’s forward channel is positive and negative 12V.
Here, the Ericsson DC/DC power module PKC2131PI is used to provide isolated positive and negative 12V and +5V, while the MICREL company’s MIC2211-2.5/3.3BML type dual output LDO is used to provide CS89712 with 3.3V and 2.5V. Figure 3 shows the CS89712 dual power supply circuit:
2. Memory Design
This system uses FLASH to store programs and parameters, and SDRAM as the program’s runtime space for data and stack. The CS89712 has a built-in SDRAM controller and memory interface. The FLASH part uses 2 pieces of Intel TE28F320B3BA110, forming a 32-bit wide 8MB FLASH; SDRAM uses 2 pieces of NEC uPD-4564163G5, forming a 32-bit wide 16MB SDRAM, as shown in Figure 4:
3. LCD Hardware Expansion Design
The liquid crystal display (LCD) has advantages such as rich information display, low power consumption, small size, and light weight, which cannot be compared with other displays. It is currently widely used in smart instruments and low-power electronic products.
The CS89712 has a built-in LCD controller, which acts as the graphics card of the embedded system. The interface has the following signals: DD［0:3］ (data line), FRM (frame synchronization signal), CL1 (line synchronization signal), CL2 (pixel data clock), M (AC bias signal). Here we expand an STN color LCD, which provides an 8-bit data interface. Table 1 shows the corresponding wiring table of the CS89712 and the LCD control signals.
4. Touch Screen Hardware Expansion Design
The touch screen input part consists of a touch screen and a touch screen controller. Together with the LCD, it can realize a complete human-computer interaction interface. Figure 7 shows the actual touch screen input system part, using a four-wire resistive touch screen. The touch screen controller adopts T［(BB) company ADS7846, which can be directly connected to CS89712 via SPI interface.
5. Ethernet Interface Design
Since the CS89712 integrates the CS8900A Ethernet controller, which has an 802.3 MAC engine, buffer, serial EEPROM interface, and 10BASE-T analog front end, only an I/O isolation filter and RJ45 interface need to be added. This circuit part is shown in Figure 8:
6. Data Acquisition Hardware Expansion Design
MAX125 is a high-speed 2X4 channel synchronous sampling 14-bit successive approximation A/D converter chip produced by MAXIM. Its analog input range is ±5V, with an internal 2.5V reference power supply and four sample/hold amplifiers (T/H). The inputs are divided into A and B groups, and by switching the switch, eight channels can be sampled. The converted digital quantities are stored in a 4X14 RAM.
Its parallel interface data access and bus release timing characteristics are compatible with the CS89712 chip bus characteristics, so the two can be directly connected without waiting for the status. Since MAXI25 is powered by +5V, when connecting to the CS89712 with an I/O power supply voltage of 3.3V, a bus level conversion chip 74LVC245A is required, which uses read and write control signals to control the bus conversion direction. After the conversion is completed, the CS89712’s external interrupt EINT1 is automatically requested, and the A/D data is read, which will automatically cancel the interrupt. By adding clipping protection, voltage following, and filtering input circuits in the forward channel, the design of the analog data acquisition circuit can be completed.
Tax Control Cash Register Application Example
1. Tax Control Cash Register Based on S3C44B0
1. Uses embedded CPU (S3C44B0)
2. Change the current high-end machines (composed of PC systems) cost too high and low-end machines (composed of microcontroller systems) resource shortage situation from the system structure, so that embedded systems can be widely used in tax control cash registers.
2. Tax Control Cash Register Composition Block Diagram
3. Hardware Composition of Tax Control Cash Register
1. CPU: S3C44B0
2. Memory: FLASH, SDRAM, NAND FLASH
3. Display: LCD, VFD
4. Touch Screen: Four-wire resistive touch screen
5. PS/2 Peripheral Interface: Keyboard, Barcode Scanner, Magnetic Card Scanner
6. RS232, Parallel Port Expansion Interface: Realized by peripheral expansion chips
7. Network Expansion Interface
8. Power Module: Mainboard power supply, MODEM power supply, VFD power supply, etc.
4. POS Software Composition
1. Operating System
1）Uses uCLinux operating system, no MMU support required, kernel can be trimmed
2）Includes a complete TCP/IP protocol stack, PPP dial-up network
2. Graphics System
Uses MiniGUI, developed by Chinese, beautiful interface, easy to transplant
3. Application Program
1）Commercial Function Module
2）Tax Control Function Module
3）Report Function Module
4）Management Settings Function Module
5）Other Function Modules
Source: Power Network
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