NXP Semiconductors MC908QB4CPE

Overview

MC908QB4CPE from Freescale Semiconductor is an 8-bit M68HC08 core microcontroller with 4 KB on-chip FLASH memory, 192 B RAM, and integrated peripherals including ADC10, AWU, ESCI, SPI, TIM, KBI, and COP watchdog. It operates at up to 8 MHz bus frequency, supports internal/external clock sources, and targets low-power embedded control in industrial sensors and appliance subsystems.

For engineers reviewing the MC908QB4CPE datasheet, MC908QB4CPE pinout, MC908QB4CPE application, or MC908QB4CPE equivalent, this page delivers verified technical context, package mapping, security byte configuration guidance, and validated alternative options for design-in and replacement decisions.

Technical Context

The MC908QB4CPE implements the M68HC08 CPU core with 16-bit address space, Harvard architecture, and 59-instruction set optimized for compact code and deterministic timing. Its memory map includes 4 KB FLASH (user-programmable, block-protectable), 192 B RAM, and 128 B EEPROM-equivalent data storage via FLASH emulation.

Peripherals include a 10-bit ADC with 8 input channels, Auto Wakeup Module with programmable sleep intervals, ESCI supporting LIN 1.3 master/slave, SPI with master/slave mode, 16-bit TIM with input capture/output compare, and keyboard interrupt module with 8 configurable inputs. Security is enforced via 8-byte monitor-mode entry key stored at $FFF6–$FFFD.

Key Specifications

Pinout & Package

MC908QB4CPE is housed in a 28-pin PDIP (Plastic Dual In-line Package), 0.6-inch body width, through-hole mount, RoHS-compliant lead finish. Pinout conforms to MC68HC908QB8/QB4 family layout with shared signal assignments across variants.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 8-bit microcontroller applications.

Compared with MC908QB4CPE, MC908QB8CPE offers double the FLASH for larger firmware while maintaining full pin and code compatibility, whereas MC908QY8CDTE trades through-hole convenience for SOIC manufacturability and wider temperature range - both serve distinct volume-production trade-offs.

Availability

MC908QB4CPE is available at Aetrix Electronics and suitable for industrial sensor nodes, home appliance control panels, automotive body modules, and smart power outlets requiring stable component supply and long-term obsolescence management.

Supply support for MC908QB4CPE 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 MCU architectures for cost-sensitive, low-power embedded systems with robust industrial qualification.

The MC68HC908QB4 belongs to the M68HC08 family designed for appliance control, sensor interfacing, and automotive sub-systems where code density, interrupt latency, and mixed-signal integration are critical.

FAQ

What is the maximum bus frequency supported by the MC908QB4CPE?

The MC908QB4CPE supports a maximum bus frequency of 8 MHz. This is achieved using the internal RC oscillator trimmed to ±2% accuracy or an external crystal up to 8 MHz. The bus clock drives all peripherals and CPU execution, and timing-critical functions like ADC conversion and ESCI baud rate generation scale directly with this frequency. The MC908QB4CPE datasheet specifies timing parameters under this condition across its full operating voltage range (2.7–5.5 V).

How does the security feature work on the MC908QB4CPE during monitor mode entry?

The MC908QB4CPE enforces security during monitor mode entry by requiring eight user-defined bytes stored at memory locations $FFF6–$FFFD. When entering monitor mode, the host must transmit matching bytes; if five or more are zero, entry is denied. This prevents casual FLASH dumping. The MC908QB4CPE documentation explicitly states that these locations must be programmed-even with dummy values-to ensure security enforcement, as blank (unprogrammed) FLASH reads as $FF, not $00.

Which analog input channels are available on the MC908QB4CPE's ADC10 module?

The MC908QB4CPE's ADC10 module supports eight analog input channels mapped to PORTA0–PORTA7. Specifically, AD0–AD7 correspond to PORTA0–PORTA7 pins, with internal multiplexer selection controlled via the ADSCR register. All channels share a common 10-bit successive-approximation converter, and the module supports single-ended sampling with programmable sample time and conversion trigger sources (software, timer, or external event). No dedicated VREF pins are required-the ADC uses VDD and VSS as reference unless externally buffered.

Can the MC908QB4CPE operate from an internal RC oscillator without external components?

Yes, the MC908QB4CPE can operate fully from its internal RC oscillator without any external crystal or capacitor. The RC oscillator is factory-trimmed and supports bus frequencies of 1 MHz, 2 MHz, 4 MHz, and 8 MHz, selectable via the CONFIG register. Internal trimming achieves ±2% accuracy over temperature and voltage, sufficient for UART communication at 9600 bps and general-purpose timing. External crystals are optional for higher precision or LIN compliance.

What low-power modes does the MC908QB4CPE support, and how do they differ?

The MC908QB4CPE supports Wait and Stop modes. In Wait mode, the CPU halts but clocks remain active-peripherals like TIM, AWU, and IRQ continue operating, enabling wake-on-event with sub-µs latency. In Stop mode, all clocks halt except the AWU counter; only RESET, IRQ, or AWU expiration can wake the device, achieving ~0.5 µA typical current draw. Both modes preserve RAM and register contents. The MC908QB4CPE's LVI circuit remains active in Stop mode to detect brown-out conditions.