Features
- 32MHz Renesas RL78-S3 CPU core
- 128KB and 256KB code flash memory with 8KB SRAM
- 4KB data flash memory
- 20-pin to 64-pin package lineup including LSSOP, LQFP, and LFQFP packages
- High-accuracy ±1.0% high-speed on-chip oscillator (HOCO)
- Security function: Prohibition of block erase and rewriting
- UART, SPI, and I2C communication interfaces
RL78/G21 Block Diagram
Description
The RL78/G21 microcontroller (MCU) has the lowest run current rate in the RL78 family, delivering exceptional power efficiency for home appliances, industrial equipment, and consumer applications. Featuring a high-accuracy ±1.0% high-speed on-chip oscillator (HOCO) and 4KB data flash memory, the RL78/G21 MCU reduces the need for external components and lowers overall system cost. The optimized built-in peripheral functions combined with hardware and software compatibility with RL78/G13 and RL78/G23 MCUs enable efficient reuse of existing design assets to reduce development efforts and accelerate time-to-market.
Parameters
| Attributes | Value |
|---|---|
| Program Memory (KB) | 128, 256 |
| Data Flash (KB) | 4 |
| RAM (KB) | 8 |
| Carrier Type | Full Carton (Tray), Full Tray (Tray), Magazine, Tape & Reel |
| Supply Voltage (V) | 1.6 - 5.5 |
| I/O Ports | 17, 29, 41, 45, 59 |
| Temp. Range (°C) | Ta = -40 to +105 |
| Operating Freq (Max) (MHz) | 32 |
| USB FS (host ch/device ch) | ( 0 / 0 ) |
| SCI or UART (ch) | 4 |
| SPI (ch) | 2, 3, 4, 5, 6 |
| I2C (#) | 2, 4, 5, 6, 7 |
| CAN (ch) | 0 |
| CAN-FD (ch) | 0 |
| Wireless | No |
| LIN (#) | 1 |
| 16-Bit Timer (ch) (#) | 8 |
| 12-Bit A/D Converter (ch) | 0 |
| 10-Bit A/D Converter (ch) | 6, 8, 10, 12 |
| 24-Bit Sigma-Delta A/D Converter (ch) | 0 |
| 12-Bit D/A Converter (ch) | 0 |
| 10-Bit D/A Converter (ch) (#) | 0 |
| 8-Bit D/A Converter (ch) | 0 |
| Capacitive Touch Sensing Unit (ch) | 0 |
| Segment LCD Controller | No |
| Security & Encryption | Unique ID, TRNG |
Product Comparison
 |  |  | |
| RL78/G21 | RL78/G13 | RL78/G23 | |
| Main CPU | RL78-S3 | RL78-S2 | RL78-S3 |
| Operating Freq (Max) (MHz) | 32 | 32 | 32 |
| Supply Voltage | 1.6 - 5.5 | 1.6 - 5.5 | 1.6 - 5.5 |
| Program Memory (KB) | 128, 256 | 16, 32, 48, 64, 96, 128, 192, 256, 384, 512 | 96, 128, 192, 256, 384, 512, 768 |
| RAM (KB) | 8 | 2, 3, 4, 8, 12, 16, 20, 24, 32 | 12, 16, 20, 24, 32, 48 |
| Data Flash (KB) | 4 | 0, 4, 8 | 8 |
| Lead Count (#) | 20, 32, 44, 48, 64 | 20, 24, 32, 48, 80 | 30, 32, 40, 44, 48, 52, 64, 80, 100 |
Application Block Diagrams
 | Corded Hand Mixer Efficient, powerful corded hand mixer system with smart control and built-in safety features. |
 | Household Water Pump Smart water pump system with low power use, noise reduction, and enhanced safety for efficient operation. |
 | Smart Remote-Controlled Tankless Gas Water Heater Tankless gas water heater with remote control, compact two-chip MCU design, and precise temperature control. |
Additional Applications
- Home Appliances
- Industrial Automation
- Consumer Electronics
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- Manual - HardwareAI-generated Summary: The RL78/G21 is a general-purpose microcontroller in the RL78 family for embedded system development. The hardware manual provides detailed information on the RL78/G21 architecture and hardware functions, including peripheral functions, registers, electrical characteristics, and other information needed for system design and application development.
- DatasheetPDF 799 KB R01DS0517EJ0100 Rev.1.00 May 20, 2026AI-generated Summary: The RL78/G21 is a general-purpose microcontroller in the RL78 family, designed for low-power embedded applications. This datasheet provides the electrical characteristics, memory and peripheral functions, pin configurations, package information, and other specifications needed to design systems using the RL78/G21.
- Application NoteAI-generated Summary: The RL78/G23 hardware design guide details essential hardware design considerations including typical circuit schematics, power supply circuits, oscillator circuits, I/O port recommendations, A/D converter notes, and on-chip debug circuits. It emphasizes proper component selection and placement, such as bypass capacitors with good frequency characteristics, and wiring patterns for power supply pins to ensure stable operation. The guide also covers power supply timing requirements, reset pin usage, and external component recommendations to optimize device performance and reliability. It includes a minimum external components list and cautions on unused pin connections and package-specific soldering instructions.
- Manual - Software
- DatasheetPDF 799 KB R01DS0517EJ0100 Rev.1.00 May 20, 2026AI-generated Summary: The RL78/G21 is a general-purpose microcontroller in the RL78 family, designed for low-power embedded applications. This datasheet provides the electrical characteristics, memory and peripheral functions, pin configurations, package information, and other specifications needed to design systems using the RL78/G21.
- Manual - HardwareAI-generated Summary: The RL78/G21 is a general-purpose microcontroller in the RL78 family for embedded system development. The hardware manual provides detailed information on the RL78/G21 architecture and hardware functions, including peripheral functions, registers, electrical characteristics, and other information needed for system design and application development.
Recommended Documents (2)
- DatasheetPDF 799 KB R01DS0517EJ0100 Rev.1.00 May 20, 2026AI-generated Summary: The RL78/G21 is a general-purpose microcontroller in the RL78 family, designed for low-power embedded applications. This datasheet provides the electrical characteristics, memory and peripheral functions, pin configurations, package information, and other specifications needed to design systems using the RL78/G21.
Datasheets (1)
- Manual - HardwareAI-generated Summary: The RL78/G21 is a general-purpose microcontroller in the RL78 family for embedded system development. The hardware manual provides detailed information on the RL78/G21 architecture and hardware functions, including peripheral functions, registers, electrical characteristics, and other information needed for system design and application development.
- Manual - Software
Manuals & Guides (2)
- Application NoteAI-generated Summary: The RL78/G23 hardware design guide details essential hardware design considerations including typical circuit schematics, power supply circuits, oscillator circuits, I/O port recommendations, A/D converter notes, and on-chip debug circuits. It emphasizes proper component selection and placement, such as bypass capacitors with good frequency characteristics, and wiring patterns for power supply pins to ensure stable operation. The guide also covers power supply timing requirements, reset pin usage, and external component recommendations to optimize device performance and reliability. It includes a minimum external components list and cautions on unused pin connections and package-specific soldering instructions.
Application Notes & White Papers (1)
Product Notices (PCN, EOL, etc) (1)
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Renesas Boards & Kits
Evaluation
RL78/G21 General-Purpose MCU Fast Prototyping Board
FPB-RL78G21 Active
Evaluate the RL78/G21 MCU and start building prototypes for smart home appliances, industrial automation, and consumer electronics. Equipped with on-chip debugging emulators and rich interfaces, enables developers to have design flexibility and easily expand design features.
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- IDE and Coding ToolRenesas integrated development environment (IDE) [Support MCU/MPU: RH850, V850, RX, RL78, 78K0R, 78K0] (Note: CS+ is not generally promoted to U.S. and European customers.) (Note: To use Smart Configurator on CS+ for RL78/G23 and RX family MCUs, install the Smart Configurator for each MCU family separately downloading from ”Design & Support” > ”Development Tools” > ”Smart Configurator”)
- IDE and Coding ToolEclipse-based Renesas integrated development environment (IDE).
- Compiler/AssemblerC Compiler Package for RL78 Family [IDE: CS+, e² studio]
- Solution ToolkitRL78 Smart Configurator is a utility for combining software in ways that meet your needs. It simplifies the embedding of Renesas drivers in your systems through supports for importing middleware and drivers and configuring pins.
- EmulatorOn-chip debugging emulator. Also available as a flash memory programmer. [Support MCU/MPU: RA, RE, RH850, R-Car D1, RL78, RX, RISC-V MCU]
- EmulatorOn-chip debugging emulator. Also available as a flash memory programmer. [Support MCU/MPU: RA, RE, RH850, RL78, RX, RISC-V MCU]
- Programmer (Unit/SW)On-chip debugging emulator available as a flash memory programmer [Available flash programming software: Renesas Flash Programmer] [Support MCU/MPU and devices: RE, RX, RL78, RH850, RISC-V MCU, Power Management, Renesas USB Power Delivery Family, ICs for Motor Driver/Actuator Driver]
- Programmer (Unit/SW)On-chip debugging emulator available as a flash memory programmer [Available flash programming software: Renesas Flash Programmer] [Support MCU/MPU and devices: RX, RL78, RISC-V MCU, Power Management, Renesas USB Power Delivery Family, ICs for Motor Driver/Actuator Driver]
- Programmer (Unit/SW)Flash memory programmer [Programming software: Dedicated GUI-based software, the "FP6 Terminal"] [Support MCU/MPU and devices: RA, RE, RX, RL78, RH850, RISC-V MCU, Renesas Synergy, Power Management, Renesas USB Power Delivery Family, ICs for Motor Driver/Actuator Driver, SuperH RISC engine, V850, 78K, R8C]
- Programmer (Unit/SW)Flash memory programming software [Support MCU/MPU and devices: RA, RE, RX, RL78, RH850, RISC-V MCU, Renesas Synergy, DA1453x, DA1459x, DA1469x, DA1470x, DA148xx, Power Management, Renesas USB Power Delivery Family, ICs for Motor Driver/Actuator Driver, V850, 78K0R, 78K0]
- SimulatorRight online tools to support initial evaluation of the low power consumption RL78 Family. Lineup: MCU Simulator Online and Current Consumption Calculator. Free of charge.
- SimulatorSimulator for RL78 Family, 78K0R and 78K0 [Support IDE: CS+] (Note: This product is included in the Compiler Package and is not available separately.)
- SimulatorSimulator for RL78 Family [Support IDE: e² studio] (Note: This product is included in the Renesas IDE "e² studio" and is not available separately.)
- ITRON OSμITRON Specification real-time OS for RL78 Family [Required IDE : CS+]
- Plug-in, OS Aware Debugging, Etc.Features for task level debugging of real-time OS applications [Plugin for Renesas IDE CS+] [Support MCU/MPU: RX, RL78]
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- IDE and Coding ToolRenesas integrated development environment (IDE) [Support MCU/MPU: RH850, V850, RX, RL78, 78K0R, 78K0] (Note: CS+ is not generally promoted to U.S. and European customers.) (Note: To use Smart Configurator on CS+ for RL78/G23 and RX family MCUs, install the Smart Configurator for each MCU family separately downloading from ”Design & Support” > ”Development Tools” > ”Smart Configurator”)
- IDE and Coding ToolEclipse-based Renesas integrated development environment (IDE).
- Compiler/AssemblerC Compiler Package for RL78 Family [IDE: CS+, e² studio]
- Solution ToolkitRL78 Smart Configurator is a utility for combining software in ways that meet your needs. It simplifies the embedding of Renesas drivers in your systems through supports for importing middleware and drivers and configuring pins.
- EmulatorOn-chip debugging emulator. Also available as a flash memory programmer. [Support MCU/MPU: RA, RE, RH850, R-Car D1, RL78, RX, RISC-V MCU]View More
Software & Tools (15)
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- Development ToolUniversal third-party programmers support a wide range of Renesas programmable devices across both off-board and on-board programming modes.Provided By: Elnec s.r.o.
- Development ToolProvides high-volume automated programming systems engineered for factory-scale production, enabling efficient handling of a wide range of integrated circuit (IC) devices. Optimized for microcontrollers (MCUs) and flash memory, the systems support tube, tape, and tray input/output configurations for flexible manufacturing integration. Advanced auto-teach alignment capabilities and robust Manufacturing Execution System (MES) integration via API protocols support streamlined operations. Scalable multi-site programming enables higher throughput while helping reduce manual intervention and minimize errors.Provided By: DediProg Technology Co., Ltd.
- Development ToolThe AH-480 automated programming system is built around a patented rotary robotic arm equipped with dual-sided vacuum nozzles, enabling high-speed, high-precision IC pick-and-place operations. The system integrates 16 units of the latest LEAP universal programmers to deliver stable, high-throughput programming performance. Designed for mass production, it combines optimized electronic controls with a robust mechanical design to support a wide range of IC types, package formats, and capacities. This integrated approach helps ensure efficient, scalable, and cost-effective programming for high-volume manufacturing environments.Provided By: LEAP ELECTRONIC CO., LTD.
- Development ToolProvides universal device programming systems combining algorithms, process-control software, and socket modules for Renesas microcontroller production. Enables high-volume programming across the RA, RX, RL78, RH850, RZ, R8C, V850, M16C, H8, H8SX, H8S, SH, 78K and Synergy families using 9th- and 10th-generation universal site technology. Supports new socket/algorithm development for devices for manual, semi-automatic, and automatic programmers.Provided By: BPM Microsystems
- Development ToolBSMART delivers a versatile, portable interfacing solution for seamless operation on silicon devices anytime and anywhere. Its compact, pocket-sized design supports both laboratory and on-site interventions. Managed via Ethernet LAN, USB-UART, or Bluetooth® through the BSMART App, it interfaces with microprocessors and serial memories using standard communication protocols or CAN/CAN-FD/LIN bus. With FlashRunner 2.0 technology, BSMART improves programming speed, configurability, and durability within the Renesas ecosystem.Provided By: SMH Technologies S.r.l.View More
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