NXP Semiconductors MC68HC908JB12DW

Overview

MC68HC908JB12DW from Freescale Semiconductor is an 8-bit HCS08 microcontroller with 12 KB on-chip FLASH, 384 B RAM, and integrated USB transceiver (D+/D–), housed in a 28-pin SOIC package operating from 3.3 V VREG. It features keyboard interrupt, two-channel timer modules, SCI UART, and low-voltage inhibit for industrial control and embedded USB peripherals.

For engineers reviewing the MC68HC908JB12DW datasheet, MC68HC908JB12DW pinout, MC68HC908JB12DW application, or MC68HC908JB12DW equivalent, key selection factors include its 28-pin SOIC footprint, USB pullup configuration via PULLEN/USBEN registers, 12 KB FLASH memory map ($CA00–$F9FF), and absence of the dual clock generator module present in the JB16 variant.

Technical Context

The MC68HC908JB12DW implements the M68HC08 CPU core with 64 B control/status registers and executes code from user FLASH ($CA00–$F9FF) and monitor ROM ($FA00–$FFFF). Its USB interface uses open-drain D+/D– pins with software-selectable 1.5 kΩ pullups to VREG or 5 kΩ to VDD, controlled by PULLEN ($001A), USBEN ($0038), and PTExP ($001D) registers.

Unlike the MC68HC908JB16, the JB12DW omits the dual 27-MHz clock generator module-registers $0051–$0059 are unimplemented-and supports only the base system integration module, SCI, keyboard interrupt, and break modules. All electrical specs match the JB16 except USB reset timing (≥125 µs low pulse required).

Key Specifications

Pinout & Package

MC68HC908JB12DW is supplied in a 28-pin Small Outline Integrated Circuit (SOIC) package with standard 0.3-inch body width and 1.27 mm pitch. Pin assignments follow the MC68HC908JB16 28-pin layout, excluding CGM-specific pins (CGMXFC1/2, CGMOUT1/2, VREGA0/A1, VSSA0/A1, VDDA).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MC68HC908JB16DW and MC9RS08KB12CW, the MC68HC908JB12DW uniquely balances native USB integration, 12 KB FLASH, and omission of unused CGM circuitry-making it the most cost-effective and pin-efficient choice for dedicated USB peripheral controllers in 28-pin SOIC.

Availability

MC68HC908JB12DW is available at Aetrix Electronics and suitable for industrial keypad controllers, USB human interface devices, serial-to-USB bridges, and embedded firmware updater modules requiring stable component supply across extended production cycles.

Supply support for MC68HC908JB12DW 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) was a leading designer of embedded processors, analog, and mixed-signal ICs for automotive, industrial, and consumer applications.

The MC68HC908JB12DW belongs to the HCS08 family-engineered for cost-sensitive, USB-enabled embedded peripherals requiring integrated transceivers, keyboard scanning, and robust in-system programmability.

FAQ

What is the FLASH memory size and address range of the MC68HC908JB12DW?

The MC68HC908JB12DW contains 12,288 bytes (12 KB) of user FLASH memory mapped from address $CA00 to $F9FF. This space stores application firmware and is programmable in-system via the monitor ROM bootloader. The MC68HC908JB12DW does not include the additional 4 KB found in the JB16 variant ($BA00–$C9FF), confirming its 12 KB total capacity.

Does the MC68HC908JB12DW support native USB device functionality?

Yes, the MC68HC908JB12DW integrates a full-speed low-speed (LS) USB transceiver with dedicated D+ and D– pins (PTE3 and PTE4). It supports USB device enumeration using software-configurable 1.5 kΩ pullups to VREG, eliminating the need for external PHY components. The MC68HC908JB12DW implements USB endpoints 0, 1, and 2 per its block diagram and memory-mapped USB module.

What is the function of the VREG pin on the MC68HC908JB12DW?

The VREG pin on the MC68HC908JB12DW delivers a regulated 3.3 V output derived from the internal voltage regulator. It powers core logic, the USB transceiver, and supplies current to the 1.5 kΩ pullups on PTE3/D+ and PTE4/D– when configured via USBEN and PTExP registers. The MC68HC908JB12DW's LVI circuit monitors this rail, triggering reset if voltage falls below 1.9 V (min).

How does the MC68HC908JB12DW differ from the MC68HC908JB16DW in terms of clock generation?

The MC68HC908JB12DW omits the dual 27-MHz clock generator module entirely-registers $0051 through $0059 are unimplemented and related functionality is absent. In contrast, the MC68HC908JB16DW includes this module for independent clock sourcing. This makes the MC68HC908JB12DW simpler and lower-cost for applications that rely solely on the primary oscillator (OSC1/OSC2) and internal bus clock.

What package type and pin count does the MC68HC908JB12DW use?

The MC68HC908JB12DW is packaged in a 28-pin Small Outline Integrated Circuit (SOIC) with standard 0.3-inch body width and 1.27 mm lead pitch. Its pinout matches the 28-pin variant of the MC68HC908JB16, excluding CGM-specific signals (CGMXFC1/2, CGMOUT1/2, analog supply pins), making it mechanically and electrically compatible for drop-in replacement where CGM is unused.