Source: https://mokxi.com/boards/attiny85 Updated: 2026-09-27 Board # ATtiny85 simulator, the chip in the breadboard Mokxi models the ATtiny85 as what it is: a bare eight-pin chip that pushes into the breadboard across the center channel. Six I/O pins, timer 0 and the high-speed timer 1, a four-channel ADC, the USI, INT0 and the pin-change interrupt, 512 bytes of SRAM and 8 KB of flash, on the internal 8 MHz oscillator. Wire the supply yourself, because nothing else will. Sign up free - 7 peripheral areas modeled - 3 projects ready to run - Real time on your own machine Click to open it in the editor The board is running real firmware right now. Click it to open the circuit in the editor. The model ## What is modeled Taken from the board's own contract document and put in plain words, with what is missing listed underneath. Core The tinyAVR instruction set, with the datasheet cycle count of every instruction. No MUL, no JMP, no CALL: this part has none of them, and reaching for one is an illegal opcode here as it is on silicon Port B PB0 to PB4 with the internal pull-ups, and PB5 held as the reset pin Timer 0 All four waveform modes, including hardware PWM on PB0 and PB1 Timer 1 The high-speed timer: OCR1C as TOP, a fourteen-entry prescaler, and complementary outputs on two pairs of pins ADC Four channels with the 1.1 V and 2.56 V references, measured against the supply the chip is actually on USI The shift register, the four-bit counter and the datasheet clock table, three-wire mode driving DO Interrupts, EEPROM and sleep INT0 on PB2, the pin-change interrupt on every pin, 512 bytes of EEPROM, and SLEEP that really does park the core ### Not in the model - The 64 MHz PLL. PLLCSR reports a lock so firmware that waits for one gets going, but timer 1 keeps counting at the system clock. - The analog comparator, the watchdog, the clock prescaler and the differential ADC channels with their gain stages. - The USI in two-wire mode as a bus driver: it counts, shifts and reports start and stop conditions, but it does not drive SDA. - The ATtiny25 and ATtiny45, which are the same part with less memory, and the ATtiny84 and friends, which are not. Start here ## Open one and press Run Each of these opens in the editor exactly as it is drawn here. Projects ## Every built-in project on the ATtiny85 Each has its own page with the circuit running, the code and a parts list. - ATtiny85 dimmer Libraries ## Arduino libraries that compile as they are Paste a tutorial that includes one of these and it builds: each is written for Mokxi, on its own drivers, under the name the tutorials use. For any other library the build names the Mokxi header that does the same job. Servo.h attach, write, writeMicroseconds, read, detach, on any pin Wire.h I2C as a master; Wire.begin() puts it on PB0 (SDA) and PB2 (SCL) SPI.h transfer and transactions, on the board’s usual SPI pins EEPROM.h read, write, update, get, put and EEPROM[i], kept in the chip’s own 512 bytes of EEPROM LiquidCrystal_I2C.h the 16x2 LCD behind its I2C backpack DHT.h the DHT11 and DHT22; one reading printed fits, but the whole heat-index tutorial is bigger than the 8 KB of flash HX711.h the HX711 load cell amplifier: tare, set_scale and get_units, the units as floats you can print ## Questions Is it free? Yes. Every board and every part is on the free plan, with no account needed. Why does it need a supply wired when the other boards do not? Because it is a chip, not a board. There is no regulator and no USB socket on an ATtiny85: pin 8 wants 5 V and pin 4 wants ground, and until they have them nothing runs. That is also why it works on 3.3 V: wire it to 3.3 V and its logic levels and its ADC reference move with it. How does the serial monitor work with no USART? The chip bit-bangs 8N1 on PB3 and PB4, and Mokxi watches those two pins the way a USB-serial adapter clipped to them would. Printing costs real time: about a millisecond a byte at 9600 baud, exactly as it does on the bench. Will my sketch run on a real ATtiny85? Yes. Every register is at its datasheet address and the firmware runtime is ours rather than the Arduino core, so a build from here runs on a real part with the CKDIV8 fuse unprogrammed. Which ATtiny? The ATtiny85, in the 8-pin DIP package. Also here ## The other boards Every one of these runs today, and every one is free. Looking for the shorter introduction? See the ATtiny85 simulator page. ESP32-C3-DevKitM-1 runs now A RISC-V core at 160 MHz with GPIO, UART, the SYSTIMER, a twelve-bit ADC on GPIO 0 to 4 and LEDC PWM on any pin, on the real memory map. Firmware for the modeled peripherals uses the board’s memory map. The contract also marks register addresses inside the SAR ADC and LEDC that are still unverified. Open the board page Arduino Uno R3 runs now A complete ATmega328P, with three timers in every mode, USART0, the ADC, interrupts and sleep. Blink, serial, a held button and a hardware PWM fade, at 16 MHz and real time. Open the board page Arduino Nano runs now The Uno's ATmega328P on a board 45 by 18 mm, so it pushes into the breadboard instead of standing beside it. Two more analog inputs than an Uno, and the same firmware runs on both. Open the board page Arduino Mega 2560 runs now The big Arduino: fifty-four digital pins, sixteen analog inputs and four serial ports, on the ATmega2560. Everything an Uno sketch knows how to do, with enough pins left over to do it to twelve things at once. Open the board page Arduino Leonardo runs now An Uno-shaped board whose USB goes to the chip itself: Serial is a USB CDC endpoint and Serial1 is pins 0 and 1. The ATmega32U4 with its ten-bit timer, fourteen ADC channels and five external interrupts, at 16 MHz. Open the board page ESP32-C6-DevKitC-1 runs now A second RISC-V board: thirty-one GPIOs, 512 KB of SRAM in one window, UART0, the SYSTIMER, a twelve-bit ADC on GPIO 0 to 6 and LEDC PWM on any pin. The contract says plainly which addresses come from the manual, which are believed rather than verified, and what is not modeled at all. Open the board page ESP32 DevKit V1 runs now The classic ESP32 on an Xtensa LX6 at 240 MHz: the GPIO matrix, UART0, timer group 0, a twelve-bit ADC1 and the eight LEDC PWM channels, on the real memory map. One core where the chip has two, no radio and no FPU. Your own sketch compiles in the tab. Open the board page ESP32-S3-DevKitC-1 runs now The ESP32-S3 on an Xtensa LX7 at 240 MHz: GPIO matrix, UART0, USB serial, ADC1, LEDC PWM and the RMT driving the RGB LED, on the real memory map. One core where the chip has two, no radio and no FPU. Your own sketch compiles in the tab. Open the board page ESP8266 NodeMCU V1.0 runs now The Xtensa LX106 at 80 MHz in the call0 ABI, with D0 to D8 that are not GPIO numbers, two active-low LEDs, and PWM done in software because the chip has none. WiFi uses a simulated network, with no radio or real internet. The ADC is the one block whose registers are this model’s own, because Espressif never published the chip’s. Open the board page Raspberry Pi Pico runs now RP2040 on our own ARMv6-M core, with SIO GPIO, the 1 MHz timer and alarms, UART0 and eight PWM slices. Blink, a button, serial and a fade at real time, with sleep parked on WFI. Open the board page Raspberry Pi Pico W runs now The same RP2040 and the same forty pins as the Pico, so the same ELF runs on it. The CYW43439 is not modeled. WiFi uses a simulated network, and the on-board LED is driven through the board runtime rather than GP25. Open the board page Seeed XIAO SAMD21 runs now A thumbnail-sized Cortex-M0+ at 48 MHz: eleven pads, every one of them an analog input, with PWM on ten of them. Serial is the chip’s own USB, modeled as a byte pipe with no stack above it, and Serial1 is a real USART on D6 and D7. Open the board page BBC micro:bit V2 runs now The nRF52833 on our own Cortex-M4 core at 64 MHz, with GPIO, GPIOTE, three TIMERs, RTC0 and UARTE0 on the real register map. The 5x5 LED matrix scanned as the hardware scans it, buttons A and B, the speaker and three rings on the edge connector. Open the board page STM32F411 Black Pill runs now Cortex-M4 with Thumb-2, NVIC and SysTick at 84 MHz, with GPIO, TIM2 to TIM5 and USART1 on the real register map. Blink on PC13, a button, serial and a PWM fade, all at real time. Open the board page STM32 Blue Pill (F103) runs now Cortex-M3 at 72 MHz, with GPIO on the F1’s CRL and CRH, TIM1 to TIM4, USART1 and a twelve-bit ADC. Blink on PC13, a button, serial with a live reading, and a PWM fade, all at real time. Open the board page Arduino Uno R4 Minima runs now Renesas RA4M1, Arm Cortex-M4 at 48 MHz, in an Uno’s shape and on an Uno’s 5 V pins. Modeled: the PFS port block, GPT PWM on the six tilde pins, SCI2 as Serial1 on D0 and D1, and a fourteen-bit ADC that analogRead reads ten bits of. Not modeled: a USB stack (Serial is a byte pipe with no enumeration behind it), the ICU, so there is no attachInterrupt, and the AGT. The contract says plainly which addresses come from the manual and which are believed rather than verified. Open the board page Arduino Pro Mini runs now The Uno’s ATmega328P on the smallest Arduino there is, with no USB on it, in both builds: 5 V at 16 MHz and 3.3 V at 8 MHz. The 3.3 V board really runs at 8 MHz, so a sketch built for 16 MHz keeps half time on it, as it does on the bench. Open the board page Arduino Micro runs now The Leonardo’s ATmega32U4 on a board that pushes into a breadboard, with the L LED on pin 13 and the SPI pins on holes of their own. Serial is the chip’s own USB and Serial1 is pins 0 and 1, and the Leonardo’s programs run on it unchanged. Open the board page SparkFun Pro Micro runs now The ATmega32U4 in a Pro Mini’s footprint with a USB socket on the end, running the Leonardo’s programs. No LED on pin 13: its lamps are RX and TX, lit by pulling their pins low. Open the board page Wemos D1 mini runs now The NodeMCU’s ESP8266 on a board a third the size, with the same D0 to D8 names and only the holes that do something. WiFi on a simulated network, and your own sketch compiles in the tab. Open the board page ESP-01S runs now An ESP8266 with eight pins, four of them GPIO, and a blue LED that lights when its pin is low. Wired with jumpers, because its two rows will not sit in a breadboard. WiFi is simulated. Open the board page Seeed XIAO ESP32-C3 runs now The ESP32-C3 at 160 MHz on the XIAO’s thumbnail outline: fourteen pads, and D0 to D10 that are the XIAO’s numbers, not GPIOs. No user LED to blink, WiFi on a simulated network, and sketches that compile in the tab. Open the board page ESP32-C3 SuperMini runs now The smallest ESP32-C3 board in common use, sixteen pins named by GPIO, at 160 MHz. Its blue LED on GPIO 8 lights when the pin is LOW, the other way around from the DevKit’s. Open the board page Arduino Uno R4 WiFi runs now The Uno R4’s RA4M1 with a 12 x 8 LED matrix to draw on through Arduino_LED_Matrix.h. WiFi through WiFiS3.h on a simulated network: no radio, no ESP32-S3 in the model, no real internet. Open the board page ## Try it on your own firmware What you build here runs on the board on your desk, unchanged. Nothing to install and no account needed. Start building Open the editor