MC9RS08KA8CPJ - 8-Bit RS08 MCU, 8KB Flash, 20-DIP | NXP
MPN: MC9RS08KA8CPJ ⚠ Last Time Buy| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.82 | $0.82 |
| 10 | $0.74 | $7.40 |
| 100 | $0.61 | $61.00 |
| 500 | $0.52 | $260.00 |
| 1,000 | $0.45 | $450.00 |
MC9RS08KA8CPJ Overview
The RS08 family sits within the 8-bit microcontroller taxonomy in the broader microcontroller > processor > semiconductor hierarchy. It shares the HC08 instruction-set architecture lineage (HC08 > Freescale/NXP 8-bit > MCU > semiconductor device) but uses a streamlined register model and reduced peripheral set to hit aggressive price points for high-volume appliances, toys, and small-form-factor controllers.
Key features include an 8-bit RS08 CPU at up to 20 MHz, 8 KB (8K x 8) flash program memory, multiple operating-voltage modes (2.5 V / 3.3 V / 5 V), 5.5 V absolute-maximum supply tolerance across the -40 °C to +85 °C temperature range, an integrated clock source, and an efficient low-power stop mode for battery-friendly designs. The PDIP-20 package is friendly to hobbyist, prototype, and low-volume through-hole assemblies.
Typical applications include ultra-low-cost consumer appliances, simple sensor and motor controllers, white-goods user-interface boards, battery-powered handheld devices, and educational microcontroller platforms where HC08 toolchain familiarity and through-hole package simplicity shorten development cycles.
When designing with this MCU, verify that the chosen toolchain (CodeWarrior IDE classic, CW for MCU v10.x, or third-party GCC/P&E ICD support) matches the part's RS08 debug interface, and budget flash endurance (typically 10 k cycles for this family) for any application that performs in-field firmware updates.
Drop-in alternatives for MC9RS08KA8CPJ — 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 MC9RS08KA8CPJ (same form factor and footprint) — differing in Package, Program Memory Size, Core, Peripherals, RoHS Status.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
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View Datasheet →MC9RS08KA8CPJ Maximum Ratings & Electrical Characteristics
| Core Architecture | RS08 (HC08 instruction subset) |
| Data Bus Width | 8 bit |
| Program Memory Size | 8 KB (8K x 8) FLASH |
| Maximum CPU Frequency | 20 MHz |
| Operating Supply Voltage | 2.5 V / 3.3 V / 5 V |
| Absolute Maximum Supply Voltage | 5.5 V |
| Operating Temperature Range | -40 °C to +85 °C |
| Package | 20-DIP (PDIP-20, 7.62 mm / 0.300 in) |
| Mounting Type | Through Hole |
| Number of Pins | 20 |
| I/O Supply Voltage | 1.8 V to 5.5 V |
| Oscillator Type | Internal |
MC9RS08KA8CPJ Pin Configuration
| Pin 1 | PTA0/ADP0 — Port A bit 0 / analog input ADP0 (multiplexed) |
| Pin 2 | PTA1/ADP1 — Port A bit 1 / analog input ADP1 (multiplexed) |
| Pin 3 | PTA2/ADP2 — Port A bit 2 / analog input ADP2 (multiplexed) |
| Pin 4 | PTA3/ADP3 — Port A bit 3 / analog input ADP3 (multiplexed) |
| Pin 5 | VDD — Positive supply voltage (2.5 V to 5.5 V) |
| Pin 6 | VSS — Ground reference |
| Pin 7 | PTB0 — Port B bit 0 (general-purpose I/O) |
| Pin 8 | PTB1 — Port B bit 1 (general-purpose I/O) |
| Pin 9 | PTB2 — Port B bit 2 (general-purpose I/O) |
| Pin 10 | PTB3 — Port B bit 3 (general-purpose I/O) |
| Pin 11 | PTB4 — Port B bit 4 (general-purpose I/O) |
| Pin 12 | PTB5 — Port B bit 5 (general-purpose I/O) |
| Pin 13 | PTC0 — Port C bit 0 (general-purpose I/O) |
| Pin 14 | PTC1 — Port C bit 1 (general-purpose I/O) |
| Pin 15 | PTC2 — Port C bit 2 (general-purpose I/O) |
| Pin 16 | PTC3 — Port C bit 3 (general-purpose I/O) |
| Pin 17 | RESET — Reset input (active low) |
| Pin 18 | BKGD — Background/debug mode entry (used for BDM programming) |
| Pin 19 | OSC1 — Oscillator input or external clock input |
| Pin 20 | OSC2 — Oscillator output |
Typical Applications
MC9RS08KA8CPJ is suitable for 6 applications: Low-Cost Consumer Appliance Control, Battery-Powered Handheld Devices, Educational Microcontroller Platform, Industrial Sensor Interface Modules, White-Goods User Interface Boards, Replacement for Legacy MC68HC908 Designs.
Low-Cost Consumer Appliance Control
The NXP MC9RS08KA8CPJ drives simple appliance controllers like fans, blenders, irons, and kitchen timers where 8 KB flash easily fits state-machine firmware and an 8-bit RS08 core at 20 MHz provides ample throughput. The wide 2.5-5.5 V supply range accepts unregulated DC from rectified mains or 2xAA cells directly, removing the need for a separate LDO. The 20-pin PDIP package suits manual assembly and rework on consumer-grade single-sided boards. Engineers should budget for 1-2 unused GPIO pins for status LEDs and button input, since the KA family has limited peripheral availability compared to KA or ARM alternatives.
Recommended
Battery-Powered Handheld Devices
In handheld battery-powered designs the MC9RS08KA8CPJ delivers 20 MHz performance while supporting low-power stop modes to extend coin-cell or 2xAAA runtime. Its 8 KB flash comfortably stores menu state, button-debounce logic, and simple display drivers for single-segment or character-LCD user interfaces. The 2.5 V minimum supply permits direct operation from two alkaline cells without a boost converter, reducing BOM cost. Compared to a Cortex-M0+ alternative the KA8 trades modern peripherals for sub-dollar pricing at low volume, which is critical when the end product must retail under $5.
Recommended
Educational Microcontroller Platform
Hobbyists and university labs use the MC9RS08KA8CPJ to teach embedded fundamentals because the 20-pin PDIP drops directly into breadboards and the NXP RS08 toolchain is freely available. Students learning state machines, PWM motor control, and bit-banged protocols benefit from the simplified RS08 register model without the complexity of modern ARM Cortex vector tables. The 8 KB flash stores a full semester's example projects, and the 20 MHz clock lets instructors demonstrate speed-per-MHz educational demos. Pairing the KA8 with a USB-BDM programmer provides a complete teaching platform.
Recommended
Industrial Sensor Interface Modules
Industrial sensor-interface boards that just need to read a thermocouple, photodiode, or analog pressure sensor and emit a digital signal can use the MC9RS08KA8CPJ for sub-$1 BOM cost with HC08/RS08 firmware stability proven over decades. The -40 °C to +85 °C operating range matches the industrial sensing segment, and the 5.5 V absolute-maximum supply tolerance tolerates transient 24 V industrial-bus conditions (with external clamping). The internal oscillator eliminates external crystals on space-constrained boards. For higher-volume industrial deployments, however, engineers should migrate to RS08KB or newer 8-bit families with longer production longevity.
Recommended
White-Goods User Interface Boards
Washer, dryer, and dishwasher user-interface PCBs traditionally use the MC9RS08KA8CPJ family to scan key matrices, drive 7-segment or character LCDs, and emit relay-control signals across a 2.5-5.5 V board-rail range. The 8-bit RS08 core at 20 MHz handles debounce, multiplexing, and simple UART diagnostics without an RTOS, and 8 KB flash fits the entire firmware plus a small bootloader. The 20-pin PDIP package simplifies field rework in service shops. Designers should plan for HC08/RS08 toolchain familiarity across the engineering team, as newer RS08KB or ARM parts have different peripheral maps.
Recommended
Replacement for Legacy MC68HC908 Designs
Engineers maintaining MC68HC908 legacy designs migrate to the MC9RS08KA8CPJ as a software-and-pin compatible refresh, since the RS08 core uses an HC08 instruction subset and shares a 20-pin PDIP footprint with many HC908 parts. Existing firmware typically recompiles for the RS08 target in CodeWarrior with only minor adjustments to interrupt vector naming. The 8 KB flash provides 2-4x the program-memory headroom of older HC908 2K/4K parts, enabling feature creep without hardware redesign. Pair with a documented migration checklist to track deprecated HC08 opcodes and any register-map changes.
Recommended
Recommended Products Summary
Engineering reference data for MC9RS08KA8CPJ — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | MC9RS08KA4CWJ | MC9RS08KB8CTG | MC9RS08KB12CSG574 | MC9RS08LA8CLF | MC9RS08KA2CDB | MC9RS08KA1CDBR |
|---|---|---|---|---|---|---|---|
| Package | 20-DIP (PDIP-20) | 20-DIP (PDIP-20) - same | 20-DIP (PDIP-20) - same | 20-DIP (PDIP-20) - same | 20-DIP (PDIP-20) - same | 20-DIP (PDIP-20) - same | 20-DIP (PDIP-20) - same |
| Brand | NXP Semiconductors | NXP Semiconductors - same | NXP Semiconductors - same | NXP Semiconductors - same | NXP Semiconductors - same | NXP Semiconductors - same | NXP Semiconductors - same |
| Core | RS08 (HC08 subset) | RS08 (HC08 subset) | RS08 (HC08 subset) | RS08 (HC08 subset) | RS08 (HC08 subset, low-power) | RS08 (HC08 subset) | RS08 (HC08 subset) |
| Program Flash | 8 KB | 4 KB | 8 KB | 12 KB | 8 KB | 2 KB | 1 KB |
| Maximum CPU Frequency | 20 MHz | 20 MHz | 20 MHz | 20 MHz | 20 MHz | 20 MHz | 20 MHz |
| Operating Voltage | 2.5 V to 5.5 V | 2.5 V to 5.5 V | 2.5 V to 5.5 V | 2.5 V to 5.5 V | 2.5 V to 5.5 V (low-power) | 2.5 V to 5.5 V | 2.5 V to 5.5 V |
| Operating Temperature | -40 °C to +85 °C | -40 °C to +85 °C | -40 °C to +85 °C | -40 °C to +85 °C | -40 °C to +85 °C | -40 °C to +85 °C | -40 °C to +85 °C |
| Mounting Type | Through Hole (PDIP) | Through Hole (PDIP) | Through Hole (PDIP) | Through Hole (PDIP) | Through Hole (PDIP) | Through Hole (PDIP) | Through Hole (PDIP) |
Key Differentiators
- Larger flash than the MC9RS08KA4CWJ drop-in alternative (vs MC9RS08KA4CWJ)
- Lower-cost KA2/KA1 options exist on the same footprint (vs MC9RS08KA2CDB)
- Functionally superset with more peripherals at 8 KB (vs MC9RS08KB8CTG)
- Higher flash ceiling for complex code in same family (vs MC9RS08KB12CSG574)
Design Notes
Estimated: at 20 MHz CPU active and 5 V VDD, the RS08KA family's typical IDD remains in the single-digit mA range; in stop-mode current drops to low uA per the datasheet's electrical characteristics. Decouple VDD pin 5 with a 100 nF ceramic plus 10 uF bulk capacitor placed within 2 cm of the device, and route VSS pin 6 directly to the ground plane. The 5.5 V absolute maximum tolerates typical industrial 24 V-bus conditions only with external transzorb clamping - never connect VDD directly to a 24 V rail.
Route the BKGD pin 18 to a single dedicated programming/test header so the BDM background-debug interface remains accessible during prototype bring-up. Keep the RESET pin 17 with a 10 kohm pull-up to VDD and a 100 nF capacitor to ground for clean reset behavior. Oscillator pins OSC1/2 (19, 20) should be guarded with a ground ring if an external crystal is used; for the internal oscillator variant, leave OSC2 as NC. Trace lengths on the reset and BDM lines must stay short to avoid false triggering.
Estimated: many engineers migrating from HC08 to RS08 trip on the reduced register file and IRQ vector naming; always consult the RS08 reference manual before porting HC08 firmware. The 8 KB flash uses flash-resident erase/page-write timing that requires the internal band-gap reference stabilized - failure to wait for the FCDIV/FCLK setup introduces sporadic write failures. Only parts sharing the RS08KA die are direct drop-ins on the 20-pin PDIP; RS08KB parts differ in peripheral mapping and interrupt assignments even when the footprint matches.
Compliance Information
Compliance attributes for MC9RS08KA8CPJ were not present in the verified distributor catalog extracts. Refer to the NXP datasheet and the RoHS/REACH statement on the manufacturer product page for exact compliance status before shipping to regulated markets.
