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.
- 7peripheral areas modeled
- 3projects ready to run
- Real timeon your own machine
What is modeled
Taken from the board's own contract document and put in plain words, with what is missing beside it.
Modeled
- 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 modeled
- 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 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.
Open one and press Run
Each of these opens in the editor exactly as it is drawn here.
Every built-in project on the ATtiny85
Each has its own page with the circuit running, the code and a parts list.
Arduino libraries that compile as they are
Paste a tutorial that includes one of these and it builds. For any other library, the build names the Mokxi header that does the same job.
And 1 more, 9 in all: HX711.h.
Tutorials that use this board
Each one ends in a running circuit, on this same board.
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.
The other boards
Every one of these runs today, and every one is free.
Looking for the shorter introduction? See the ATtiny85 simulator page.
A RISC-V chip at 160 MHz, on the real memory map.
The classic Arduino, with an ATmega328P running at 16 MHz.
The Uno’s chip on a small board that fits a breadboard.
The big Arduino, with 54 digital pins and four serial ports.
An Uno-shaped board whose chip does its own USB serial.
A second RISC-V board, with 31 pins and simulated WiFi.
The classic ESP32 at 240 MHz, with simulated WiFi.
The ESP32-S3 at 240 MHz, with USB serial and an RGB LED.
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.