MC908QT4ACDWER

The MC908QT4ACDWER from NXP Semiconductors is a compact, low-cost 8-bit microcontroller in the HC08 QT family, designed for applications requiring minimal I/O count and program memory. Built on the M68HC08 CPU core, this device delivers up to 8MHz bus speed and features 4KB of in-application programmable Flash memory and 128 bytes of RAM. Despite its small 8-pin SOIC package, the MC908QT4 packs a surprising amount of functionality including a 4-channel 8-bit ADC, a 16-bit timer with two channels supporting input capture, output compare, and PWM modes, and a keyboard interrupt module for wake-up from low-power modes. The internal trimmable oscillator eliminates the need for external crystal components, reducing total system cost and board space. The Flash memory supports in-application programming (IAP), allowing firmware updates in the field through a simple two-wire interface. System reliability features include a COP watchdog timer, low-voltage detection (LVD), and illegal opcode/address reset detection. With only 5 general-purpose I/O pins but flexible peripheral multiplexing, the MC908QT4 is an ideal solution for replacing discrete components in simple control applications, providing more functionality and flexibility than analog or logic alternatives at a comparable cost. Typical applications include simple sensor interfaces, appliance controls, battery chargers, LED dimming, fan control, and any low-cost embedded function where a small MCU adds intelligence without adding significant cost.

The MC908QT4 is built around the M68HC08 CPU08 core, an 8-bit CISC processor that executes the HC08 instruction set. The CPU fetches instructions from Flash memory and executes them using its arithmetic logic unit (ALU), index registers, and stack pointer. Program execution can be interrupted by hardware interrupts from peripherals (ADC, timer, keyboard, etc.) or by reset sources (power-on, COP watchdog, low-voltage detect). The internal clock module provides a trimmable internal RC oscillator that generates the system clock without external components, which can be factory-trimmed for accuracy. The 8-bit ADC uses a successive approximation register (SAR) architecture to convert analog voltages on its 4 input channels to digital values, with 8-bit resolution. The 16-bit timer/PWM module (TIM) provides two channels that can be independently configured for input capture (measuring pulse widths), output compare (generating timed events), or pulse-width modulation (controlling motor speed, LED brightness, etc.). The keyboard interrupt module monitors up to 6 I/O pins for level changes and can generate an interrupt to wake the MCU from low-power stop or wait modes, enabling efficient power management in battery-operated applications. In stop mode, all clocks are halted and current consumption drops to microamp levels, while wait mode halts the CPU but keeps peripherals running for faster wake-up response. Flash memory programming is performed through the monitor ROM (MON08) interface or by the application code itself (in-application programming), using the on-chip charge pump to generate the high voltages needed for Flash erase and program operations.

Note: Pins are multiplexed with multiple peripheral functions. Exact pin function is configured through port configuration and module control registers. Pin 4 (PTA3/RST) is the default reset pin and can be configured as a general-purpose I/O when the reset function is disabled. The OSC1/OSC2 pins can be used for external crystal/ceramic resonator or as GPIO when using the internal oscillator.

• Simple Sensor Interfaces: Ideal for temperature, light, and analog sensor interfaces where the 8-bit ADC provides basic measurement capability and the MCU handles calibration and signal processing
• Appliance Control: Used in small appliances such as coffee makers, toasters, and humidifiers for temperature control, timing functions, and user interface
• Battery Chargers: Implements simple charging algorithms with voltage and current sensing via the ADC, and PWM control of charging current
• LED Lighting Control: Provides PWM-based dimming control for LED lights, strips, and fixtures, with analog input for brightness adjustment
• Discrete Component Replacement: Replaces discrete logic circuits, timers, and analog control circuits with a single MCU for reduced BOM cost and board space
• Fan Speed Control: Implements closed-loop or open-loop fan speed control using the PWM output and timer peripherals
• Keypad Interfaces: Manages pushbutton inputs with the keyboard interrupt module, providing debouncing and wake-on-press functionality
• Power Supply Sequencing: Monitors power supply voltages with the ADC and LVD, and controls power-up/down sequencing for multi-rail systems