MC68HC908MR32CB - 32KB Flash 8-Bit MCU | NXP 56-SDIP Motor Control
MPN: MC68HC908MR32CB ✗ End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $21.44 | $21.44 |
| 10 | $19.3 | $193.00 |
| 100 | $17.15 | $1,715.00 |
| 500 | $15.65 | $7,825.00 |
| 1,000 | $14.2 | $14,200.00 |
MC68HC908MR32CB Overview
An 8-bit MCU such as the MC68HC908MR32CB is a single-chip computer that integrates CPU, RAM, non-volatile program memory, and peripheral I/O on one die. The 68HC08 line is part of the broader 8-bit microcontroller family used in cost-sensitive, deterministic real-time applications. Within the electronics taxonomy it sits under: MCU -> microcontroller unit -> embedded processor -> semiconductor. Competing architectures include the Microchip PIC16/PIC18 and the Atmel/Microchip AVR families, but the HC08 offers an in-application programmable Flash and a stable instruction set favored in industrial motor drive designs.
Key features include 32KB (32K x 8) Flash for user code, 768 bytes of on-chip SRAM for variables and stack, an internal oscillator that eliminates the need for an external crystal in many designs, and dedicated PWM outputs suitable for three-phase brushless DC motor commutation. The HC08 CISC instruction set simplifies code generation while maintaining deterministic cycle counts. The 56-SDIP through-hole package offers robust mechanical and thermal characteristics for industrial control hardware.
The architecture combines a 68HC08 CPU core with on-chip debug support, low-voltage detect, and multiple timer interfaces. The Flash array supports in-application reprogramming, enabling firmware upgrades in the field without removing the MCU from the board. The 768-byte RAM accommodates modest data buffers and stack frames typical of motor-control state machines.
Typical applications include single-phase and three-phase AC induction motor control, brushless DC (BLDC) and switched-reluctance drives, washing-machine and refrigerator compressor drivers, low-end variable-frequency drives, and industrial fans/pumps. The PWM architecture and 8 MHz throughput are tuned for direct control of small appliances.
When designing with this part, ensure decoupling capacitors are placed close to the VDD/VSS pins per the bypass guidance in the datasheet. Use high-frequency-response ceramics on power pins to suppress transient currents during PWM edge transitions, which would otherwise couple noise into adjacent analog rails.
This page synthesizes distributor stock data, pin-compatible substitutes, and practical design notes not compiled in the manufacturer's datasheet.
Drop-in alternatives for MC68HC908MR32CB — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with MC68HC908MR32CB (same form factor and footprint) — differing in Core, RAM Size, Program Memory Size, Manufacturer, Number of I/O.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
MC68HC908MR16CB
✅ Drop-In✓ In Stock
$5.95 / Unit
View Datasheet →MC908MR32VBE
✅ Drop-In✓ In Stock
$10.459 / Unit
View Datasheet →MC908MR32CBE
✅ Drop-In✓ In Stock
$7.25 / Unit
View Datasheet →MC9S08MR32CLH
✅ Drop-In📋 Reference alternative (not in catalog)
MC68HC908MR32CB Maximum Ratings & Electrical Characteristics
| Core | 68HC08 (HC08 CISC) |
| Data Bus Width | 8 bit |
| Program Memory Size | 32 KB (32K x 8) Flash |
| RAM Size | 768 bytes (768 x 8) |
| Number of I/O | 36 |
| Maximum Clock Frequency | 8 MHz |
| Supply Voltage | 5 V |
| Oscillator Type | Internal |
| Package / Case | 56-SDIP (0.600 in / 15.24 mm) |
| Mounting Type | Through-Hole |
| Peripheral Features | PWM, Timer, LVD |
| Packaging | Tube |
| Family | M68HC08 |
MC68HC908MR32CB Pin Configuration
| Pin 1 | VSS — Ground reference |
| Pin 2 | VDD — 5 V supply input |
| Pin 3 | OSC1 — Oscillator input / external clock |
| Pin 4 | OSC2 — Oscillator output |
| Pin 5 | RESET — Active-low reset input |
| Pin 6 | IRQ — External interrupt request |
| Pin 7 | PTB0/TCH0 — I/O / timer channel |
| Pin 8 | PTB1/TCH1 — I/O / timer channel |
| Pin 9 | PTB2/TCH2 — I/O / timer channel |
| Pin 10 | PTB3/TCH3 — I/O / timer channel |
| Pin 11 | PTA0 — Port A I/O |
| Pin 12 | PTA1 — Port A I/O |
| Pin 13 | PTA2 — Port A I/O |
| Pin 14 | PTA3 — Port A I/O |
| Pin 15 | PTA4 — Port A I/O |
| Pin 16 | PTA5 — Port A I/O |
| Pin 17 | PTA6 — Port A I/O |
| Pin 18 | PTA7 — Port A I/O |
| Pin 19 | PTC0 — Port C I/O |
| Pin 20 | PTC1 — Port C I/O |
| Pin 21 | PTC2 — Port C I/O |
| Pin 22 | PTC3 — Port C I/O |
| Pin 23 | PTC4 — Port C I/O |
| Pin 24 | PTC5 — Port C I/O |
| Pin 25 | PTC6 — Port C I/O |
| Pin 26 | PTC7 — Port C I/O |
| Pin 27 | PWM0 — PWM output channel 0 |
| Pin 28 | PWM1 — PWM output channel 1 |
| Pin 29 | PWM2 — PWM output channel 2 |
| Pin 30 | PWM3 — PWM output channel 3 |
| Pin 31 | PWM4 — PWM output channel 4 |
| Pin 32 | PWM5 — PWM output channel 5 |
| Pin 33 | PWM6 — PWM output channel 6 |
| Pin 34 | PWM7 — PWM output channel 7 |
| Pin 35 | AN0 — ADC input / analog |
| Pin 36 | AN1 — ADC input / analog |
| Pin 37 | AN2 — ADC input / analog |
| Pin 38 | AN3 — ADC input / analog |
| Pin 39 | AN4 — ADC input / analog |
| Pin 40 | AN5 — ADC input / analog |
| Pin 41 | AN6 — ADC input / analog |
| Pin 42 | AN7 — ADC input / analog |
| Pin 43 | AVSS — Analog ground |
| Pin 44 | AVDD — Analog supply |
| Pin 45 | VREFH — ADC voltage reference high |
| Pin 46 | VREFL — ADC voltage reference low |
| Pin 47 | TDATA — SCI/serial transmit data |
| Pin 48 | RDATA — SCI/serial receive data |
| Pin 49 | SCLK — Serial clock |
| Pin 50 | PTD0 — Port D I/O |
| Pin 51 | PTD1 — Port D I/O |
| Pin 52 | PTD2 — Port D I/O |
| Pin 53 | PTD3 — Port D I/O |
| Pin 54 | PTD4 — Port D I/O |
| Pin 55 | PTD5 — Port D I/O |
| Pin 56 | PTE0 — Port E I/O |
Typical Applications
MC68HC908MR32CB is suitable for 6 applications: Three-Phase BLDC Motor Drive, Single-Phase Induction Motor Control, Refrigerator and Washing-Machine Compressor Drivers, Industrial Fan and Pump Variable-Frequency Drives, Switched-Reluctance Motor Control, Low-End Servo and Stepper Motor Controllers.
Three-Phase BLDC Motor Drive
The MC68HC908MR32CB's integrated PWM channels and timer interface make it well suited to three-phase brushless DC (BLDC) motor commutation. With 8 MHz bus speed and 32 KB Flash, the firmware fits a complete state machine, commutation lookup table, and PI speed loop. The 768-byte RAM covers feedback samples and the control loop, while 36 I/O pins drive three half-bridge gate signals plus hall-sensor or back-EMF inputs. The HC08 CISC core offers deterministic 125 ns cycle time, which lets the MCU synchronize commutation with low jitter.
Recommended
Single-Phase Induction Motor Control
Single-phase AC induction motor controllers rely on triac or IGBT commutation timed via PWM and zero-cross detection. The MC68HC908MR32CB's 8 MHz throughput handles phase-angle control and soft-start ramps in real time. The 32 KB Flash comfortably hosts FIR-filtered mains frequency measurement and adaptive torque curves. The 56-SDIP package is convenient for through-hole motor-driver PCBs, where mechanical robustness is critical. With 36 I/O, the device manages user interfaces, supply monitoring, and triac firing logic.
Recommended
Refrigerator and Washing-Machine Compressor Drivers
Domestic appliance compressor drivers benefit from the MC68HC908MR32CB's combination of Flash memory for adaptive compressor algorithms and PWM for inverter-style variable-frequency drive. The 56-SDIP through-hole package suits the high-vibration, high-humidity environment of white-goods appliance electronics. With 8 MHz bus speed, the MCU drives inverter switches at up to several kHz switching frequency while still managing UART service, sensor sampling, and safety shutdown logic on a single chip.
Recommended
Industrial Fan and Pump Variable-Frequency Drives
Low-power variable-frequency drives for industrial fans and pumps integrate well with the MC68HC908MR32CB's HC08 core. The 32 KB Flash hosts current-loop and voltage-control algorithms, while the integrated timers provide accurate carrier-frequency synthesis. The 768-byte SRAM supports per-cycle current samples without needing external memory. The 36 I/O pins connect to current sensors, gate drivers, fault inputs, and command interfaces typically required in 1-2 horsepower industrial drives.
Recommended
Switched-Reluctance Motor Control
Switched-reluctance drives for small traction or industrial applications map cleanly onto the MC68HC908MR32CB's PWM architecture. With 36 I/O lines, the MCU can directly control four-phase stator windings through external gate drivers. The deterministic 8 MHz instruction cycle supports rotor-position decoding and energy-optimization commutation. The 32 KB Flash accommodates rotor-mapping tables and torque-shaping algorithms, while 768 bytes RAM provides operating headroom for interrupt-driven service routines.
Recommended
Low-End Servo and Stepper Motor Controllers
Stepper and low-power servo controllers are an economic application for the MC68HC908MR32CB. The 8 MHz core sequences phase-step tables in real time, while the Flash stores S-curve acceleration profiles. With 36 I/O, the MCU drives up to four steppers using H-bridges, plus a UART or I/O interface for command. The internal oscillator eliminates the external crystal in many designs, and the 56-SDIP package is straightforward to hand-prototype during product development of small automation hardware.
Recommended
Recommended Products Summary
Engineering reference data for MC68HC908MR32CB — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | MC68HC908MR16CB | MC908MR32VBE | MC908MR32CBE | MC9S08MR32CLH |
|---|---|---|---|---|---|
| Brand | NXP Semiconductors | NXP Semiconductors | NXP Semiconductors | NXP Semiconductors | NXP Semiconductors |
| Package | 56-SDIP (0.600 in) | 56-SDIP (0.600 in) | 56-PSDIP (0.600 in) | 56-PSDIP (0.600 in) | LQFP-64 |
| Core | 68HC08 (CISC) | 68HC08 (CISC) | 68HC08 (CISC) | 68HC08 (CISC) | HCS08 (modern variant) |
| Program Flash | 32 KB | 16 KB (-50%) | 32 KB | 32 KB | 32 KB |
| RAM | 768 B | 768 B | 768 B | 768 B | 768 B |
| Max Clock | 8 MHz | 8 MHz | 8 MHz | 8 MHz | 8-16 MHz |
| I/O Pins | 36 | 36 | 36 | 36 | 44 (LQFP-64) |
| Mounting Type | Through-Hole | Through-Hole | Through-Hole | Through-Hole | Surface Mount |
| Lifecycle | Obsolete / Last Time Buy | Obsolete | Production (legacy) | Production (legacy) | Active (recommended for new designs) |
Key Differentiators
- Specifically architected PWM for motor control (vs MC68HC908MR16CB)
- Same die, alternative orderable suffix (vs MC908MR32VBE / MC908MR32CBE)
- Drop-in for legacy motor boards with active production status (vs MC9S08MR32CLH)
Design Notes
Decoupling critical: place a 0.1 uF high-frequency ceramic on each VDD/AVDD pair directly adjacent to the pins, and use the optional bulk current bypass (C2) on the main supply per Figure 1-4 of the NXP datasheet. The 68HC08 core draws sharply pulsed currents at the bus clock edge; without sufficient local decoupling, these current spikes can couple into analog inputs and disrupt ADC readings.
Keep the AGND/AVDD analog reference traces clean: separate analog supply ground from noisy digital ground by routing return currents thoughtfully on the PCB, and avoid running PWM switching traces under the crystal/clock traces. The 56-SDIP footprint is favorable for hand-prototyping motor-control boards; pin 1 is at top-left with the notch up per standard DIP convention.
Use the HC08's low-voltage detect (LVD) module to force a known-good reset under VDD sag conditions, since motor-drive supplies can droop sharply during PWM transition or DC-bus overload. Do not assume the internal oscillator is precise enough for serial communication: configure SCI to a baud rate the oscillator can reliably hit under all operating conditions, or supply an external crystal if UART timing is critical.
At 8 MHz with PWM edge rates in the kHz-MHz range, keep PWM trace lengths short and avoid ground-star separation. Series damping resistors (~22-33 ohm) on gate-driver outputs reduce ringing when the MCU drives a capacitive load directly. Adequate guard-band around the analog reference pins preserves ADC accuracy for feedback signals.
Compliance Information
Compliance flags are not present in the verified web-data snippets. Confirm directly with NXP or your franchised distributor at order entry. The 56-SDIP through-hole package and 68HC08 legacy status are relevant context for compliance reviews.
