Abstract: This paper introduces an intelligent secondary instrument designed using the ADuC834 microcontroller. The hardware and software design methods of the instrument are presented, and the application methods of the ADuC834 are briefly described. Keywords: ADuC834; secondary instrument; intelligent instrument The ADuC834 is a truly complete data acquisition system chip. This novel microprocessor converter and advanced mixed-signal processing technology significantly improve the performance of the data acquisition system and greatly reduce the development time and cost of the application system. The ADuC834 is a newly launched microprocessor converter product from Analog Devices (AD). It integrates a dual-channel Σ-Δ ADC, a temperature sensor, a gain-programmable amplifier (PGA), an 8-bit 51 MCU, 62k of programmable EEPROM, 4k of data Flash Memory, 2304 bytes of on-chip RAM, a 12-bit DAC, timers, I2C-compatible SPI, and standard serial I/O. Therefore, the ADuC834 itself is a high-performance data acquisition system with an embedded MCU, which can be used to easily construct various secondary instrument systems. 1. ADuC834 Chip Introduction The ADuC834 integrates two independent Σ-Δ ADCs, with a 24-bit main ADC and a 16-bit auxiliary ADC. Due to the use of digital filtering, these two independent ADC channels can achieve wide dynamic range low-frequency signal measurement, making them ideal for applications such as weighing instruments, tension strain gauges, pressure transducers, and temperature measurement. The main channel's AD input range is divided into 8 levels between ±20mV and ±2.56V, and any level can be selected during use. Thanks to Σ-Δ conversion technology, it can achieve up to 24-bit lossless code performance, and the auxiliary channel can also be used as a temperature sensor. The ADuC834 uses a 32kHz crystal oscillator to drive the on-chip phase-locked loop (PLL) to generate the required internal operating frequency. Its microcontroller core is compatible with the 8051. On-chip peripherals include a serial port compatible with SPI and I2C, multiple digital input/output ports, a watchdog timer, a power monitor, and a time interval counter. The chip also provides 62kB of flash/electrically erasable program memory and 2304 bytes of on-chip RAM. The ADuC834 itself can provide serial program download, so debugging programs can be directly downloaded, greatly facilitating program development and design. Therefore, various complex secondary instruments can be easily constructed using the ADuC834. 2. Hardware Circuit Design of the Secondary Instrument This system design mainly focuses on sampling from two sensors, then processing the data and displaying the corresponding data, while also requiring a complex menu design. Since floating-point multiplication and division operations are used in the data processing, and a menu setting is required, the 62kB program memory space of the ADuC834 can be used for various complex calculations and processing without the need for external program memory. Figure 1 shows its hardware design schematic. This system utilizes the P3 port of the ADuC834 to construct a 3×4 keyboard, and uses the P0 and P2 ports and a 74HC138 decoder to construct a dynamic display screen with 10 seven-segment LEDs. Then, it uses the P1.0 and P1.1 ports of the ADuC834 and a 74HC164 to construct an eight-LED display. Simultaneously, the ADuC834's serial port SPI function is used for software debugging. 2.1 Dynamic Display of Seven-Segment LEDs: Using P2.0 to P2.4 of the ADuC834's P2 port, and decoding with a 74HC138, eight address strobe signals can be obtained. P2.5 and P2.6 are used to construct the remaining two strobe signals, while the P0 port is used as the data interface for the display. The program can select the self-loading mode of the ADuC834 timer T2 and set it to 2ms. The display buffer of the seven-segment LEDs can be dynamically refreshed to achieve dynamic display. 2.2 Keyboard Control Circuit The keyboard control circuit can be constructed using P3.0 to P3.6 of the ADuC834's P3 port, as shown in Figure 2. As can be seen from Figure 2, the keyboard has 12 keys in 3 rows and 4 columns, using 7 I/O lines as control lines. P3.0, P3.1, and P3.2 are used as row scan lines, and P3.3 to P3.6 are used as column return lines to form a matrix keyboard. During operation, when a key is pressed, the program does not immediately enter the key processing routine; it only enters the program processing when the key is pressed and released. This prevents key bounce and repeated key presses. 2.3 LED Design Since this system requires 8 status displays, 8 LEDs are needed to represent the different states of the current program. This can be achieved by using P1.0, P1.1, and the 74HC164 to control 8 LED displays. 3. Software Programming of Secondary Instruments 3.1 Data Acquisition Program When performing AD acquisition, the internal reference voltage of the ADuC834 can be selected (note that the internal reference voltage is Vref = 1.25V, so the input range of the ADC channels is halved). Different input ranges can be selected by writing RN2, RN1, and RN0 of the AD0CON register, and channel replacement can be performed by writing CH1 and CH0 of the AD0CON register to achieve AD sampling of the input voltage of two channels. The initial acquisition program is as follows: [align=center] [/align] 3.2 Programming of User Flash/Electrically Erasable Data Memory The user flash/electrically erasable data memory of the ADuC834 has a capacity of 4kB. This EEPROM can be used to store system configuration information. The specific program is as follows: [align=center] [/align] 4. Conclusion The hardware and software design of the secondary instrument described in this paper features fast acquisition speed, high accuracy, and small system size. It is particularly suitable for systems that require complex calculations and high acquisition accuracy with a small size. In actual design and development, using the ADuC834 can significantly shorten development time and reduce costs. In addition, the secondary instrument designed by the author has achieved good results in practical applications. References 1. ADuC834. PDF. http://www.analog.com 2. Wu Pinghui. A data acquisition device based on ADuC812 microcontroller. Electrical Measurement & Instrumentation, 2002(1) 3. Liu Shuming, et al. Principle and application of ADuC812 data acquisition system chip. Xi'an University of Electronic Science and Technology Press, 2000