NXP Semiconductors MC68HC908GT8CFB

Overview

MC68HC908GT8CFB from Freescale Semiconductor is an 8-bit HCS08-core microcontroller with 8 KB on-chip flash memory, 512 bytes RAM, and integrated peripherals including 10-bit ADC (8 channels), SPI, ESCI (UART), TIM, TBM, KBI, and COP watchdog. It operates at up to 8 MHz bus frequency, supports 2.7–5.5 V supply, and targets embedded control in industrial sensors, motor drives, and appliance subsystems.

For engineers reviewing the MC68HC908GT8CFB datasheet, MC68HC908GT8CFB pinout, MC68HC908GT8CFB application, or MC68HC908GT8CFB equivalent, key selection criteria include its 44-pin QFP package, internal clock generator with DCO+PLL architecture, flash programmability in-system, low-power STOP/WAIT modes, and hardware-based keyboard interrupt support for touch-panel interfaces.

Technical Context

The MC68HC908GT8CFB implements the CPU08 core with 16-bit address space, indexed addressing, and 72-instruction set optimized for compact code. Its Internal Clock Generator (ICG) integrates a digitally controlled oscillator (DCO), modulo-N divider, frequency comparator, and digital loop filter to achieve ±4% accuracy across voltage/temperature without external crystal.

Peripherals are tightly coupled via the System Integration Module (SIM): the ESCI provides full-duplex UART with automatic baud rate detection; the 10-bit ADC supports single- or continuous-conversion modes with software-triggered start; and the Keyboard Interrupt Module (KBI) monitors up to 8 inputs with edge-sensitive wake-up capability in STOP mode.

Key Specifications

Pinout & Package

MC68HC908GT8CFB is housed in a 44-pin Quad Flat Package (QFP) with 0.8 mm lead pitch, JEDEC MS-026 compliant, and thermally enhanced for convection-cooled industrial PCBs.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar microcontroller applications.

Compared with MC68HC908GT8CFB, MC9RS08KA8CFD offers higher core clock but sacrifices KBI and ESCI flexibility, while MC9S08QG8CDT matches pinout and peripherals but omits industrial temp rating and fine ICG trimming - making MC68HC908GT8CFB optimal for robust, feature-complete embedded control in harsh environments.

Availability

MC68HC908GT8CFB is available at Aetrix Electronics and suitable for industrial motor control, smart appliance subsystems, building automation sensor nodes, and PLC I/O expanders requiring stable component supply across long production lifecycles.

Supply support for MC68HC908GT8CFB includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Freescale Semiconductor (now part of NXP Semiconductors) pioneered 8-bit microcontroller architectures for cost-sensitive, high-reliability embedded systems in automotive and industrial markets.

The MC68HC908GT8CFB belongs to the HC08 family, designed specifically for resource-constrained control applications demanding integrated analog interfaces, low-power operation, and field-programmable flash - especially where external crystals are undesirable.

FAQ

What is the maximum operating frequency of the MC68HC908GT8CFB?

The MC68HC908GT8CFB supports a maximum bus frequency of 8 MHz, achieved via its internal clock generator's PLL-based frequency multiplication. This corresponds to approximately 2 million instructions per second (MIPS) execution speed. The ICG allows dynamic switching between internal DCO (±4% accuracy) and external crystal sources, with settling time to within 5% specified at ≤100 µs after clock change - critical for real-time control timing budgets in the MC68HC908GT8CFB.

Does the MC68HC908GT8CFB support in-system programming (ISP)?

Yes, the MC68HC908GT8CFB supports full in-system programming via its on-chip flash memory, enabling firmware updates without removing the device from the PCB. Programming is performed through the background debug mode (BDM) interface using standard Freescale BDM protocol, with page-erase (128-byte granularity) and byte-program capabilities. This capability is integral to field maintenance and calibration workflows for products incorporating the MC68HC908GT8CFB.

How does the Keyboard Interrupt Module (KBI) function in the MC68HC908GT8CFB?

The KBI in the MC68HC908GT8CFB monitors up to eight configurable input pins (PTA7–PTA0) for edge transitions and generates an interrupt without CPU polling. Each pin has independent enable/disable and edge-select (rising/falling) control. In STOP mode, KBI remains active and can wake the MCU with typical current draw of less than 1 µA - making it ideal for battery-powered touch interfaces. This hardware-accelerated scanning is a defining feature of the MC68HC908GT8CFB.

What are the ADC reference voltage options for the MC68HC908GT8CFB?

The MC68HC908GT8CFB ADC supports two reference configurations: external reference via dedicated VREFH and VREFL pins (allowing ratiometric or precision external references), or internal VDDA as reference (simplifying design when supply rail stability suffices). The 10-bit resolution yields 1,024 steps; with 5 V full-scale, LSB = 4.88 mV. Input channels are multiplexed from PTB7–PTB0, and conversion time is fixed at 16 bus cycles - a deterministic timing behavior essential for synchronized sampling in the MC68HC908GT8CFB.

Is the MC68HC908GT8CFB pin-compatible with other members of the GTx series?

The MC68HC908GT8CFB shares the same 44-pin QFP package and pin assignment with MC68HC908GT16CFB (16 KB flash variant), enabling hardware reuse across product tiers. Key signals - including all I/O ports, RST, IRQ, OSC1/OSC2, ESCI, SPI, and ADC inputs - occupy identical physical locations. However, flash size and some configuration bits differ, so firmware must be validated per variant. This compatibility simplifies migration paths within the MC68HC908GT8CFB family.