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This paper primarily explains the working principle of the serial D/AMAX521, detailing its operational sequence, connection methods with a microcontroller, and some sample programs. It also provides an in-depth analysis of the MAX521, a 2-wire, 8-channel, 8-bit voltage output digital-to-analog converter (DAC). The device features five reference voltage inputs: the first four DACs (DAC0 to DAC3) have individual reference inputs (REF0 to REF3), allowing independent voltage range settings, while the remaining four DACs (DAC4 to DAC7) share a single reference input (REF4). The MAX521 supports a serial interface with a built-in software protocol, enabling a maximum conversion frequency of up to 400 kbps. Its double-buffered input structure allows for individual or simultaneous updates of DAC registers, and it includes a low-power mode that reduces current consumption to as low as 4 μA. The chip operates on a single +5V power supply.
The MAX521 is commonly used in applications such as minimal analog device systems, data offset/sampling adjustment, industrial process control, and automatic testing equipment. It is available in multiple package types, including 20-pin DIP, 24-pin SO, and 24-pin SSOP. The pin configuration of the 20-pin DIP version is illustrated in Figure 1, showing key signals like voltage outputs (OUT0–OUT7), reference inputs (REF0–REF4), address pins (AD0, AD1), clock (SCL), data (SDA), and ground connections (DGND, AGND).
In terms of communication, the MAX521 uses the I2C bus protocol, which consists of two lines: SCL (clock) and SDA (data). The SCL line is controlled by the master device, while the SDA line is bidirectional. Data transmission follows specific timing rules, where data changes occur when SCL is low, and the start and stop conditions are defined by transitions on the SDA line while SCL is high. Each byte transferred is sent with the most significant bit (MSB) first.
The device addressing byte for the MAX521 consists of five fixed bits (01010) followed by two address bits (AD0 and AD1) and one read/write bit (R/W). A command byte follows the address, containing bits for reset (RST), power-down (PD), and channel selection (A2–A0). The ACK signal is generated by the receiver after each byte to confirm successful reception.
For interfacing with a microcontroller unit (MCU), the MAX521 is typically connected to the I2C pins of the MCU, such as P1.6 and P1.7. All reference voltages are set to +5V, ensuring the DAC output ranges from 0 to +5V. The device address is configured as 01B, and the system is designed to support multiple DAC conversions efficiently. Sample code and timing diagrams illustrate the communication process between the MCU and the MAX521.
This system has been successfully implemented in circuits requiring multiple DAC conversions, offering a cost-effective and efficient solution for intelligent device development.