A drilling pressure data acquisition system was designed and developed using the new ADuC848 microcontroller and Keil simulation software. This system features a 16-bit high-precision A/D converter, real-time data acquisition, uploading, and storage, a maximum operating temperature of 125℃, and characteristics of low power consumption and high integration. When using ISP online programming, the system software should be adjusted promptly according to field needs for flexible application. Introduction Currently, most drilling pressure measurement tools in China are imported equipment, which is costly and difficult to maintain. Existing domestic equipment has significant shortcomings in size, integration, and accuracy, and is also aging rapidly. Based on this situation, the author developed a drilling pressure data acquisition system based on the ADuC848 microcontroller with expandable acquisition channels. The ADuC848 is a newly launched microcontroller from Analog Devices (ADI) with military-grade standards, capable of supporting up to 8 analog signal input conversion channels on a single chip, and expanding to up to 16 analog input channels in master/slave mode. It features a single 16-bit high-precision A/D converter, 16-bit error-free encoding, a large-capacity 64 KB Flash ROM, 4 KB on-chip Flash, and 2304 bytes of on-chip RAM. It boasts a high-performance single-cycle core, an external crystal oscillator with a programmable frequency multiplication up to 12.58 MHz, ISP in-system high-speed download programming, 24 I/O ports, 11 interrupt sources (2 priorities), dual data pointers, an internal power-saving mode, a 12-bit D/A converter, UART, SPI, and I2C serial communication modes, a watchdog timer (WDT), and a power monitor (PSW). The ADuC848 chip's 52-pin MQFP package measures only 14 mm × 14 mm, with a maximum operating temperature of 125°C and a maximum normal operating current of 4.8 mA and a maximum power-saving mode current of 20 μA. Therefore, the ADuC848 is particularly suitable for developing small data acquisition systems that operate for extended periods in harsh, high-temperature environments. 1 System Hardware Design This system is mainly divided into 5 modules, and all major components are selected from Analog and digital military standard products from ADI, which greatly improves the system's reliability, high temperature resistance, and shock resistance. The overall block diagram of the system hardware design is shown in Figure 1. 1.1 Analog Signal Input Conditioning Module This module mainly realizes the amplification and filtering functions of the pressure sensor input signal. The front-end signal amplification section uses a high-precision, zero-drift AD8230 rail-to-rail instrumentation operational amplifier, calibrated to an amplification gain of 200 times after resistance measurement. The amplified signal is filtered by an OP07D operational amplifier and input to the ADuC8d8 analog channel for acquisition. The drilling pressure input signal is generally 0-15mV, and the signal output to the A/D acquisition after amplification and filtering is 0-3V. The operating temperature range of AD8230 is -40℃ to 125℃, the maximum drift voltage is 10μV, and the maximum temperature drift is only 50 nV/℃. This system amplifies only one analog signal for experimental purposes and has an expansion input channel interface, allowing for expansion to eight channels on a single chip as needed. The circuit schematic of this module is shown in Figure 2. 1.2 System Power Supply Module Since the downhole working power supply is generally provided by a 9-12V lithium battery, and the operating voltage of all system components is around 5V, the 9V power supply needs to be rectified to a 5V input power supply for the system. The ADP303 voltage converter used in the power supply section is a high-precision, 200mA low-drift linear rectifier, particularly suitable for power rectification in low-power systems. Its operating voltage range is 3.2-12V, which can solve the problem of system malfunction due to insufficient external voltage. Because the system components are divided into analog and digital components, the power supply is correspondingly divided into analog and digital power supplies. The rectified 5V power supply is supplied to the analog power supply and the digital power supply respectively through a 100mH inductor and a 1.8Ω resistor, which greatly reduces power supply interference to the digital components. The analog ground and digital ground also need to be filtered through a 0Ω resistor before being connected together to reduce interference, especially important for high-precision digital devices. The schematic diagram is shown in Figure 3. 1.3 SPI Real-Time Data Storage Module According to the system requirements, data needs to be stored in real-time. The SPI interface of the ADuC848 microcontroller is used to read and write to an external Flash chip to achieve data playback. Considering the special nature of drilling operations, a single continuous operation is less than 100 hours. Based on the calculation of acquiring 5 sets of 16-bit data per second, the capacity of a single Flash chip should be at least 6.86 MB. Therefore, this system uses the AT45DB542D (AT45D for short) 64 Mb serial SPI memory. The AT45DB542D Flash chip has a large storage capacity, high-speed read/write up to 66 MHz, low-power serial operation at 10 mA, can be erased and written 100,000 times, and can store data for up to 10 years. Multiple chips can be combined according to the actual situation on site, up to a maximum of 256 Mb, to fully meet the needs of large-scale data storage. This system uses a single-chip memory to complete the experiment. The schematic diagram is shown in Figure 4. 1.4 The data upload interface for the host computer communication uses RS-232 serial communication mode, with a baud rate of 9600 bps. The microcontroller's input/output level is TTL level, i.e., UART serial port, which is inconsistent with the electrical specifications of the PC's RS-232 standard serial interface. Therefore, level conversion is necessary for data communication between the control chip and the PC. The MAX232 interface conversion chip can effectively realize the communication function with the host computer. The specific implementation is shown in Figure 5. 1.5 The interface connections between the ADuC848 interface, reset, PSEN, and dual-machine expansion modules and the MCU are all completed by the peripheral circuit design of the ADuC848's I/O and communication ports. All power supply interfaces require 0.1μF capacitor filtering. The interrupt section consists of a switch and a 10 kΩ pull-down resistor to ensure timely interrupt response within the system's interrupt level tolerance. The MCU's built-in TXD and RXD ports are directly connected to the RS-232 module's Tlin and Rlout ports for serial communication. The system provides eight A/D analog input interfaces (AIN1 to AIN8) for system expansion. The system's reset circuit is implemented using a button and an RC circuit. During system operation, the REST port is kept low. When a reset is needed, the RC circuit is activated to complete a high-level reset for 16 system clock cycles. The program download mode is implemented by connecting a 1kΩ pull-down resistor to the PSEN port. When the system is in continuous operation, PSEN is in open-circuit non-download mode. When the system program needs to be updated, simply short PSEN to the 1kΩ resistor and activate the reset circuit. The system will then automatically enter download mode and wait for the host computer to download the program. The system's dual-machine expansion and external memory interfaces are implemented using the ADuC848's four-wire SPI interface (MISO, MOSI, SCLOCK, SS). By configuring the master and slave devices and selecting the data transmission/reception clock, the system can read and write to the memory and expand the MCU's functionality. The specific block diagram is shown in Figure 6. 2. Software Development and ISP Download The software development and simulation download of this system are implemented in the latest Keil uVision3 environment from Keil. Keil microcontroller application development software supports various MCS51 architecture chips from different companies, integrating editing, compilation, downloading, and simulation; it also supports PLM, assembly, and C language programming, and has powerful functions in program debugging and software simulation. Keil uVision3 supports the development and online download of ADuC8XX series chips, is easy to use, and can meet the needs of the system software development environment. The system software flowchart is shown in Figure 7, including two main functions: First, to realize continuous data acquisition, storage, and uploading under interruption requests without playback; second, to realize data playback and uploading under interruption requests. The example code for the data acquisition part is as follows: The example code for reading data from the memory is as follows: ADuC848 P2. P2.0 is connected to the memory clock SCLK, P2.1 is connected to SI, P2.2 is connected to SO, and P2.3 is connected to the CS chip select. Example code for reading data from the memory is as follows: For the ADuC848, P2.0 is connected to the memory clock SCLK, P2.1 is connected to SI, P2.2 is connected to SO, and P2.3 is connected to the CS chip select. Edited by: He Shiping