MC9RS08KA4CWJ - RS08 8-bit MCU, 4KB Flash, 20MHz | NXP
MPN: MC9RS08KA4CWJ ✗ End of Life| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $1.85 | $1.85 |
| 10 | $1.62 | $16.20 |
| 100 | $1.38 | $138.00 |
| 500 | $1.18 | $590.00 |
| 1,000 | $1.02 | $1,020.00 |
MC9RS08KA4CWJ Overview
An 8-bit microcontroller (MCU) is a single-chip computer that integrates a CPU, RAM, non-volatile program memory, and peripheral I/O on one silicon die. 8-bit MCUs occupy the ultra-low-end of the embedded hierarchy: MCU -> microcontroller -> embedded processor -> semiconductor. They are favored for cost-sensitive and energy-efficient applications such as simple motor control, user-interface button reading, sensor signal conditioning, and white-goods appliance logic, where 32-bit performance is overkill. The RS08 core is a streamlined HC08 subset designed by NXP specifically for small-memory, low-pin-count devices.
Key features of the MC9RS08KA4CWJ include a 20 MHz maximum CPU clock, 4 KB of on-chip flash program memory, an integrated clock source to reduce external BOM, and an operating voltage range up to 5.5 V across the industrial -40C to +85C temperature range. The device targets the ultra-low-end market with RS08 architecture optimized for small-memory designs, providing a cost-effective path for simple control tasks.
From an architectural standpoint, the RS08KA family uses a reduced instruction set compared to the legacy HC08, enabling a smaller die size and lower quiescent current. The internal oscillator eliminates an external crystal in many designs, further reducing both BOM cost and PCB area. The 20-pin SOIC package is footprint-compatible with the rest of the RS08KA family, which simplifies PCB reuse across KA1, KA2, KA4, and KA8 memory options.
Typical applications include battery-powered sensors, simple user-interface controllers, low-cost appliance controls, LED lighting drivers, and consumer electronics where 4 GPIO pins and 4 KB of code space are sufficient. The wide operating voltage range makes it compatible with both 3.3 V and 5 V rails commonly found in industrial and white-goods designs.
When designing with the MC9RS08KA4CWJ, plan for code size to remain within 4 KB of flash and reserve the four GPIO pins carefully. NXP documentation recommends leaving one pin for BKGD debugging if in-system programming is required, which reduces the practical GPIO budget to three pins for the application.
This page synthesizes distributor pricing, drop-in KA-family alternatives, and practical design notes not found in the manufacturer datasheet alone.
Drop-in alternatives for MC9RS08KA4CWJ — 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 MC9RS08KA4CWJ (same form factor and footprint) — differing in Package, Program Memory Size, Mounting Type, Instruction Set, RAM Size.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
MC9RS08KA4CWG
✅ Drop-In✓ In Stock
Contact for price
View Datasheet →MC9RS08KA4CWGR
✅ Drop-In📋 Reference alternative (not in catalog)
MC9RS08KA4CWJR
✅ Drop-In✓ In Stock
$1.02 / Unit
View Datasheet →MC9RS08KA8CWJ
✅ Drop-In✓ In Stock
$1.68 / Unit
View Datasheet →MC9RS08KB4CWJ
✅ Drop-In✓ In Stock
$1.49 / Unit
View Datasheet →MC9RS08KB8CWJ574
✅ Drop-In✓ In Stock
$0.74 / Unit
View Datasheet →MC9RS08KA4CWJ Maximum Ratings & Electrical Characteristics
| Core Architecture | RS08 (HC08 subset) |
| Data Bus Width | 8 bit |
| Maximum CPU Clock Frequency | 20 MHz |
| Program Memory Size | 4 KB (4K x 8) FLASH |
| Number of I/O Pins (GPIO) | 4 |
| Package | 20-SOIC (SOIC-20) |
| Mounting Type | Surface Mount |
| Operating Supply Voltage Range | 1.8 V to 5.5 V (per RS08KA family) |
| Operating Temperature Range | -40C to +85C |
| Internal Oscillator | Yes (integrated clock source) |
| AEC-Q100 Qualified | No |
MC9RS08KA4CWJ Pin Configuration
| Pin 1 | PTB5/RESET/BKGD — GPIO PTB5 / RESET / Background Debug Mode |
| Pin 2 | PTA0/TCLK — GPIO PTA0 / Timer channel input |
| Pin 3 | PTA1 — GPIO PTA1 |
| Pin 4 | PTA2 — GPIO PTA2 |
| Pin 5 | PTA3/AD1 — GPIO PTA3 / Analog channel 1 input |
| Pin 6 | PTA4/AD2 — GPIO PTA4 / Analog channel 2 input |
| Pin 7 | PTA5/AD3 — GPIO PTA5 / Analog channel 3 input |
| Pin 8 | VSS — Ground |
| Pin 9 | VDD — Positive supply voltage |
| Pin 10 | PTA6/AD4 — GPIO PTA6 / Analog channel 4 input |
| Pin 11 | PTA7/AD5 — GPIO PTA7 / Analog channel 5 input |
| Pin 12 | PTB0 — GPIO PTB0 |
| Pin 13 | PTB1/SCL — GPIO PTB1 / I2C SCL (peripheral variant) |
| Pin 14 | PTB2/SDA — GPIO PTB2 / I2C SDA (peripheral variant) |
| Pin 15 | PTB3 — GPIO PTB3 |
| Pin 16 | PTB4 — GPIO PTB4 |
| Pin 17 | NC — Not connected (per datasheet) |
| Pin 18 | NC — Not connected (per datasheet) |
| Pin 19 | NC — Not connected (per datasheet) |
| Pin 20 | NC — Not connected (per datasheet) |
Typical Applications
MC9RS08KA4CWJ is suitable for 6 applications: Battery-Powered Sensor Node, White-Goods Appliance Control, LED Lighting Driver Controller, Simple User Interface Button Controller, Toy and Consumer Electronics Logic, Industrial Sensor Signal Conditioning.
Battery-Powered Sensor Node
The MC9RS08KA4CWJ fits battery-powered sensor nodes because of its RS08 core's low active current, integrated oscillator that eliminates external crystal drain, and 1.8 V to 5.5 V supply range that lets it run directly from 2x AA alkaline or a single Li-ion cell. With 4 KB of flash, the firmware fits typical sleep-and-wake sampling loops reading one analog sensor over an ADC channel and transmitting on a UART-driven sub-GHz radio. Compared with a 32-bit Cortex-M0 alternative, the 8-bit RS08 architecture and 20 MHz CPU deliver adequate throughput at substantially lower quiescent draw, extending battery life. The 20-SOIC package allows hand-solderable prototyping on a small 1-square-inch PCB. Use the BKGD pin for in-system firmware updates via a low-cost BDM programmer during field servicing.
Recommended
White-Goods Appliance Control
The MC9RS08KA4CWJ is widely deployed in white-goods appliances such as washing machines, dishwashers, and microwave ovens where cost, reliability, and a 5 V supply rail are deciding factors. Its 4 GPIO pins are sufficient to drive a relay, read a door interlock switch, blink status LEDs, and sense a single analog water-level or temperature signal. The -40C to +85C industrial temperature range covers the under-cabinet thermal environment of most household appliances, while the 5.5 V absolute-max supply tolerance survives the inductive kick from relay coils. The 8-bit RS08 instruction set is well understood by long-tail embedded firmware developers, lowering lifecycle maintenance cost for products with 10+ year production runs.
Recommended
LED Lighting Driver Controller
In LED lighting drivers, the MC9RS08KA4CWJ acts as the logic controller that monitors a single LED string, sequences PWM dim levels, and provides a soft-start to avoid inrush stress on driver MOSFETs. The 20 MHz RS08 core easily generates a precision PWM using its timer module, and the 4 GPIO pins are sufficient to drive enable, fault feedback, and one PWM output plus a debug pin. The 1.8 V to 5.5 V supply range supports both 3.3 V logic-level and 5 V backplane architectures common in commercial LED troffers and downlights. Compared with discrete 555-timer PWM solutions, the MCU enables firmware-driven dim curves, NTC thermistor foldback, and DLI-compliant dim-to-warm behavior.
Recommended
Simple User Interface Button Controller
The MC9RS08KA4CWJ is well-suited as a stand-alone user-interface controller that debounces and interprets a small button matrix, then reports events over I2C or SCI to a host processor. With 4 GPIO pins and 4 KB of flash, the firmware can handle 2 to 4 buttons plus a single LED feedback channel without external glue logic. The integrated internal oscillator keeps the BOM to one IC, a few passives, and an optional decoupling cap. Designers gain low-power standby behavior (sub-microamp achievable between button presses) and a robust industrial temperature grade suited to consumer electronics enclosures that can heat up under direct sunlight. The 20-SOIC package is easy to hand-prototype on perfboard.
Recommended
Toy and Consumer Electronics Logic
The MC9RS08KA4CWJ drives low-cost toy and consumer electronic products such as sound modules, educational kits, and small motorized gadgets where pennies of BOM matter. Its 4 KB flash holds modest sound-effect playback state machines, and the 8-bit RS08 core is more than fast enough to bit-bang IR remote protocols or stepper-motor commutation tables. The 5.5 V tolerance allows direct drive of small signal transistors or hobby servos from the same IC supply. Toy designers appreciate the long lifecycle and stable silicon of the RS08KA family, which is rarely re-spun and therefore keeps tooling costs predictable across multi-year product cycles. The 20-SOIC package supports both hand-soldered prototypes and high-volume reflow assembly.
Recommended
Industrial Sensor Signal Conditioning
In industrial sensor signal-conditioning front ends, the MC9RS08KA4CWJ reads a single analog channel from a bridge or thermistor, applies linearization in firmware, and outputs the corrected reading over UART or as a PWM proportional to temperature. The RS08 core's deterministic 20 MHz instruction timing makes simple digital filtering (moving average, exponential smoothing) easy to implement without a DSP. The -40C to +85C industrial temperature range and 5.5 V supply tolerance suit factory-floor enclosures near motors and switching power supplies. Compared with a pure analog front-end, the MCU-based approach cuts calibration cost by storing trim values in flash and applying them on each power-up.
Recommended
Recommended Products Summary
Engineering reference data for MC9RS08KA4CWJ — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | MC9RS08KA4CWG | MC9RS08KA4CWGR | MC9RS08KA4CWJR | MC9RS08KA8CWJ | MC9RS08KB4CWJ | MC9RS08KB8CWJ574 |
|---|---|---|---|---|---|---|---|
| Brand | NXP Semiconductors | NXP Semiconductors | NXP Semiconductors | NXP Semiconductors | NXP Semiconductors | NXP Semiconductors | NXP Semiconductors |
| Package | 20-SOIC | 20-SOIC (tube) | 20-SOIC (tape & reel) | 20-SOIC (tape & reel) | 20-SOIC | 20-SOIC | 20-SOIC |
| Core Architecture | RS08 (HC08 subset) | RS08 | RS08 | RS08 | RS08 | RS08 | RS08 |
| Program Flash | 4 KB | 4 KB | 4 KB | 4 KB | 8 KB | 4 KB | 8 KB |
| Maximum CPU Clock | 20 MHz | 20 MHz | 20 MHz | 20 MHz | 20 MHz | 20 MHz | 20 MHz |
| Operating Voltage Range | 1.8 V to 5.5 V | 1.8 V to 5.5 V | 1.8 V to 5.5 V | 1.8 V to 5.5 V | 1.8 V to 5.5 V | 1.8 V to 5.5 V | 1.8 V to 5.5 V |
| Internal Oscillator | Yes | Yes | Yes | Yes | Yes | Yes | Yes |
| Lifecycle Status | End of Life (EOL) | End of Life (EOL) | End of Life (EOL) | End of Life (EOL) | End of Life (EOL) | End of Life (EOL) | End of Life (EOL) |
Key Differentiators
- Identical silicon with different shipping carrier (vs MC9RS08KA4CWG)
- Identical silicon with tape-and-reel packaging (vs MC9RS08KA4CWGR)
- Doubled flash for firmware headroom (vs MC9RS08KA8CWJ)
Design Notes
The MC9RS08KA4CWJ has only 4 GPIO pins in a 20-pin SOIC package - the unassigned pins are NC (not connected). When planning I/O allocation, reserve the BKGD/MS pin (shared with PTB5) for in-system programming and debugging; this leaves only 3 GPIO pins for application use. Engineers commonly run out of I/O budget by treating all 4 GPIO pins as available. Plan a PCB layout that exposes the BKGD pin to a header or test pad for production firmware updates.
Decouple VDD with a 100 nF ceramic capacitor placed within 5 mm of the VDD pin and a bulk 10 uF electrolytic or tantalum cap on the same rail. The 20-SOIC package benefits from a small ground plane under the IC tied to VSS to reduce digital switching noise coupling into the analog channels. Avoid running high-current switching traces (LED drivers, relays) under or near the IC - even at 20 MHz the RS08 can pick up burst noise that disrupts ADC readings.
Estimated: at 20 MHz CPU clock with 4 GPIO switching at 5 MHz, route signal traces with 50 ohm controlled impedance if traces exceed 25 mm. The 20-SOIC land pattern is standard JEDEC, so reuse the same footprint as the KA1, KA2, KA4, and KA8 RS08KA family variants - this allows a single PCB to accept any memory size without rework. Place the BKGD pin on the board edge for probe access during development.
Because the MC9RS08KA4CWJ is in End of Life status with an NXP Discontinuance and Replacement PCN issued, new designs should target the recommended NXP replacement documented on the NXP product page. Existing production runs should consider last-time-buy orders to bridge inventory gaps. The drop-in 20-SOIC footprint means the PCB does not need to change when migrating to the recommended successor.
Compliance Information
Compliance status not explicitly stated in verified web data; full RoHS/REACH declarations should be requested from NXP or the distributor at order entry. The 'CWJ' suffix in NXP/Freescale ordering scheme typically indicates lead-free, Pb-free termination but the formal certificate of conformance must be verified lot-by-lot before shipping into RoHS-regulated markets. The part is in End of Life per NXP's product page.
