NXP Semiconductors MC68HC908JB8JDW

Overview

MC68HC908JB8JDW from Freescale Semiconductor is an 8-bit HCS08 microcontroller with 8 KB on-chip FLASH, 512 B RAM, and integrated USB 1.1 low-speed device controller. It features a 20 MHz CPU bus speed, 24 I/O pins, and hardware support for keyboard interrupt (KBI), timer interface (TIM), and COP watchdog. Used in embedded USB peripherals such as industrial HID devices and diagnostic tools.

For engineers reviewing the MC68HC908JB8JDW datasheet, MC68HC908JB8JDW pinout, MC68HC908JB8JDW application, or MC68HC908JB8JDW equivalent, key selection criteria include its native USB transceiver compliance with USB 1.1 low-speed signaling, 20-pin SOIC package, 5 V operation, ROM-resident monitor for in-system programming, and lack of external memory interface - all critical for cost-sensitive, space-constrained USB endpoint designs.

Technical Context

The MC68HC908JB8JDW implements the HCS08 CPU core with enhanced addressing modes and a 16-bit index register. Its USB module integrates a full-featured transceiver with internal voltage regulator, supporting suspend/resume, endpoint 0 control transfers, and two additional endpoints (EP1/EP2) for bulk/interrupt data.

It uses a single-phase crystal oscillator (1–8 MHz) or external clock input, with internal PLL not present; bus clock derived directly from OSCXCLK via divide-by-1 or -2. The SIM provides power-on reset, LVI detection, and configurable stop/wait low-power modes with wake-up from IRQ, KBI, or USB resume.

Key Specifications

Pinout & Package

MC68HC908JB8JDW is housed in a 20-pin SOIC (case 751B-03) package with 0.300″ body width and 0.050″ lead pitch. Pin assignments are defined per Section 1.5 of the MC68HC908JB8/D Rev. 2.3 datasheet.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar microcontroller-with-integrated-USB applications.

Compared with MC68HC908JB8JDW, MC9RS08KB12CFUE trades integrated USB for larger memory and newer core, while STM32F042F4P6 offers ARM ecosystem advantages at the cost of 5 V compatibility and simplified in-field programming.

Availability

MC68HC908JB8JDW is available at Aetrix Electronics and suitable for industrial USB peripherals, embedded diagnostic tools, and legacy equipment interface modules requiring stable component supply and long-term obsolescence management.

Supply support for MC68HC908JB8JDW 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) designed high-reliability microcontrollers for automotive, industrial, and consumer applications with emphasis on integration and robustness.

The MC68HC908JB8JDW belongs to the HCS08 family, engineered for cost-sensitive, USB-enabled embedded endpoints where minimal external components, 5 V operation, and field-upgradable firmware are essential design requirements.

FAQ

What is the maximum operating frequency of the MC68HC908JB8JDW CPU core?

The MC68HC908JB8JDW CPU core runs at a maximum bus frequency of 20 MHz. This is achieved using an external crystal (1–8 MHz) or clock source fed into the OSC1 pin, with optional divide-by-1 or divide-by-2 scaling in the SIM module. The core does not include an internal PLL, so bus speed is directly derived from the oscillator input - making MC68HC908JB8JDW suitable for deterministic real-time applications without clock synthesis complexity.

Does the MC68HC908JB8JDW support in-system programming via USB?

Yes, the MC68HC908JB8JDW supports in-system programming via its integrated USB interface using the ROM-resident monitor (MON). When held in monitor mode at reset, it enumerates as a USB device and accepts FLASH erase, program, and verify commands over endpoint 0. No external programmer is required - MC68HC908JB8JDW enables firmware updates directly from a host PC using vendor-provided utilities or custom bootloader implementations.

What USB speed and device class does the MC68HC908JB8JDW support?

The MC68HC908JB8JDW implements a USB 1.1 low-speed (1.5 Mbps) device controller compliant with the USB specification for low-speed devices. It supports control transfers on endpoint 0 and data transfers on endpoints 1 and 2, but does not implement USB classes (e.g., HID, CDC) in hardware - those must be implemented in firmware. The integrated transceiver and VREG make MC68HC908JB8JDW self-contained for basic USB device functionality without external PHY components.

Can the MC68HC908JB8JDW operate from a 3.3 V supply?

No, the MC68HC908JB8JDW is specified for 4.5 V to 5.5 V operation only. Its internal USB transceiver, FLASH programming circuitry, and I/O buffers are designed for 5 V logic levels. Attempting to power MC68HC908JB8JDW from 3.3 V will result in improper USB enumeration, unreliable FLASH writes, and undefined I/O behavior. For 3.3 V systems, consider alternatives like the STM32F042F4P6 - but note that MC68HC908JB8JDW requires strict 5 V compliance.

How many I/O pins does the MC68HC908JB8JDW provide, and which ports support interrupt-on-change?

The MC68HC908JB8JDW provides 24 programmable I/O pins across Ports A–E. Port A (PTA0–PTA7) supports hardware keyboard interrupt (KBI) with individual enable/disable per pin and edge-selectable wake-up. Other ports do not offer pin-level interrupt-on-change; external interrupts are limited to the dedicated IRQ pin and USB resume event. This makes MC68HC908JB8JDW especially suited for keypad-centric applications where Port A's KBI reduces firmware overhead significantly.