**AD1674TD: The Complete Guide to Microprocessor-Compatible 12-Bit A/D Conversion**

In the realm of data acquisition, the bridge between the analog physical world and the digital domain of microprocessors is built by analog-to-digital converters (ADCs). The **AD1674TD stands as a seminal and highly integrated solution** from Analog Devices, designed specifically for seamless interfacing with microprocessor systems. This 12-bit ADC combines high performance with exceptional ease of use, making it a cornerstone component in industrial control, scientific instrumentation, and high-accuracy measurement systems.

**Architectural Overview and Key Features**

The AD1674TD is far more than a simple converter; it is a complete, **microprocessor-compatible data acquisition system on a single chip**. Its architecture integrates several critical components that would otherwise require separate ICs:

* **A 12-Bit SAR ADC:** At its core is a high-speed successive approximation register (SAR) ADC, capable of **100 kSPS (kilo-samples per second)** conversion rates. This provides a solid balance between speed and resolution for a wide range of applications.

* **On-Chip Sample-and-Hold Amplifier (SHA):** The integrated SHA captures a fast-changing analog input signal and holds it stable during the conversion process, which is critical for achieving rated accuracy, especially for dynamic signals.

* **Internal Voltage Reference:** A precision 10.0V reference is built-in, trimmed to a high level of accuracy. This eliminates the need for an external reference component, simplifying design and saving board space.

* **Three-State Output Buffers:** The digital output lines are equipped with three-state buffers, allowing the converter to **interface directly with microprocessor data buses** without the need for additional glue logic.

**Microprocessor Compatibility: The Defining Advantage**

The "TD" suffix denotes a device rated for the industrial temperature range, but the true genius of the AD1674 lies in its bus interface logic. It is designed to appear to a microprocessor as a simple memory location or I/O port.

* **Easy Interface:** It can be **directly connected to popular microprocessor buses** such as those of the 68000, 8086, 80386, and 8051 families. The converter's control logic interprets standard read/write signals to initiate conversions and output data.

* **8-Bit or 12-Bit Data Transfer:** The AD1674TD offers flexible data output modes. The 12-bit result can be read in a single 16-bit operation (with 4 pins unused) or in two 8-bit bytes, making it incredibly versatile for both 8-bit and 16-bit systems. This **two-byte read operation is a key feature for 8-bit microcontrollers**.

* **Simple Control Logic:** Conversion is started by executing a simple write command. The Status (STS) pin indicates whether a conversion is in progress, allowing the CPU to either poll for completion or use the signal to generate an interrupt.

**Application Circuit and Operation**

A typical interface circuit is remarkably simple. The analog input (which can be configured for various unipolar and bipolar ranges, e.g., 0 to +10V, ±5V, ±10V) is connected, and the digital lines are tied directly to the system data bus. Key control pins—Chip Select (CS), Read/Convert (R/C), and Address (A0)—are decoded from the system address bus.

The operational sequence is straightforward:

1. The microprocessor initiates a conversion by writing to the ADC's address (R/C pin set low).

2. The STS pin goes high, indicating the conversion has begun.

3. The microprocessor waits (via polling or an interrupt) for the STS pin to go low, signaling conversion completion.

4. The microprocessor then reads the high byte and then the low byte of the result by performing two read operations from the same address.

**Performance Considerations**

While highly integrated, designers must still adhere to good practices for maximizing performance. **Proper bypassing of power supplies** (using 0.1µF ceramic capacitors close to the pins) is mandatory to minimize noise. For the highest accuracy, attention must be paid to the analog input signal conditioning and grounding scheme to avoid noise coupling into the sensitive analog front-end.

**ICGOODFIND**

The **AD1674TD remains a classic and powerful example of a system-level ADC**. Its integration of the ADC, SHA, reference, and bus interface logic into a single 28-pin package dramatically reduces component count, design complexity, and board space. For engineers developing systems around a microprocessor or microcontroller that require robust, high-accuracy 12-bit conversion, the AD1674TD offers a proven, reliable, and elegantly simple solution.

**Keywords:**

1. **Microprocessor-Compatible ADC**

2. **12-Bit Resolution**

3. **Integrated Sample-and-Hold**

4. **Successive Approximation (SAR)**

5. **Data Acquisition System**