ATtiny 202/402
August 5, 2022 ยท View on GitHub
| Specifications | ATtiny202 | ATtiny402 |
|---|---|---|
| Flash (program memory) | 2048 bytes | 4096 bytes |
| Flash w/Optiboot | 1536 bytes | 3584 bytes |
| RAM | 128 bytes | 256 bytes |
| EEPROM | 64 bytes | 128 bytes |
| Bootloader (optional) | Optiboot Optiboot (absolutely not recommended) | Optiboot (strongly not recommended) |
| GPIO Pins | 6 (5 usable) | 6 (5 usable) |
| ADC Channels | 6 (5 usable) | 6 (5 usable) |
| DAC | No | No |
| PWM Channels | 4 | 4 |
| Timer Type B | 1 | 1 |
| Timer Type D | No | No |
| CCL Logic Blocks | 2 (no int) | 2 (no int) |
| Event Channels | 3, 1 sync 2 async | 3, 1 sync 2 async |
| Interfaces | UART, SPI, I2C | UART, SPI, I2C |
Users needing to use the event system are strongly urged to use a 2-series part or at least a 1-series part. The 0-series event system is extremely limited.
Clock Options
These parts do not support an external HF crystal, only an external clock. No watch crystal support on 0-series.
| MHz | Source | Notes |
|---|---|---|
| 20 | Internal | |
| 16 | Internal | |
| 10 | Internal | |
| 8 | Internal | |
| 5 | Internal | |
| 4 | Internal | |
| 1 | Internal | |
| 20 | Internal, tuned | |
| 16 | Internal, tuned | |
| 12 | Internal, tuned | |
| 20 | External Clock | External clock goes to CLKI (PA3). Minimize any load on this pin, including even short wires. HF stuff is very picky. |
| 16 | External Clock | As above. |
| 10 | External Clock | As above. |
| 8 | External Clock | As above. |
| 24 | Internal, tuned | OVERCLOCKED, usually fine @ 5v and room temperature. |
| 25 | Internal, tuned | OVERCLOCKED, usually fine @ 5v and room temperature. |
| 30 | Internal, tuned | OVERCLOCKED, may be unstable. |
| 24 | External Clock | OVERCLOCKED, usually fine @ 5v and room temperature. Uses CLKI/PA3 as above. |
| 25 | External Clock | OVERCLOCKED, usually fine @ 5v and room temperature. Uses CLKI/PA3 as above. |
| 30 | External Clock | OVERCLOCKED, may be unstable. Uses CLKI/PA3 as above. |
| 32 | External Clock | OVERCLOCKED, may be unstable. Uses CLKI/PA3 as above. |
| When external clock is used as system clock source, it cannot be used for any other purpose (obviously) - all control over that pin is taken by CLKCTRL. |
- The overclocked options at 24/25 MHz have been found to generally work around room temperature when running at 5v. The faster ones - while they can be stable with solid 5v supply at room temperature, this is right on the edge of what these parts can do. I have specimens that will run at 5.0v but not at 4.8, for example, meaning that it would work powered by some USB ports, but not others (those range from 4.7 to 5.3v) and they are of course extremely sensitive to noise on power rails. External oscillators work more reliably than the internal one when overclocking, but they generally cost about as much as the microcontroller itself and are gross overkill (in terms of accuracy) for what most arduino folks want from them.
The tuned options are new in 2.4.0 - see the tuned internal oscillator guide for more information before using these options.
WARNING: On pre 2.0.0 versions of megaTinyCore, the UART defaulted to the alternate positions
This matches the megaTinyCore 412/402 Rev. - and Rev. A breakout boards below. In 2.0.0 and later, this is no longer the case! You must call Serial.swap(1) prior to Serial.begin() to move it to the alt pins (or connect your adapter to pins 0 and 1 instead of 2 and 3). It should never have been done that way in the first place. A Rev. B of the breakout boards that has the FTDI header tied to the standard serial pins is planned for availability in May 2020.
Signature Issue
There exist ATtiny402's in the wild where the last byte of the signature is 0x25, instead of 0x27. Currently shipping parts from Atmel/Microchip have the correct signature, and this problem appears to be in the past, for the most part. However, if you're stuck with wrong-signature ATtiny402's, choose ATtiny402 (bad signature) from the tools -> chip menu.
The issue with bootloader
- There's no dedicated reset pin. So there is no way to do the traditional autoreset circuit to reset the chip to upload with a bootloader unless you disable UPDI (requiring HV UPDI to undo - I've got a half dozen boards that are bricked until I have time to get an HVUPDI programming setup together to resurrect them). Either you manually power cycle it just prior to trying to upload, or you have some sort of ersatz-reset solution coupled to an autoreset circuit, or handle it in some other bespoke way. Regardless of the approach, short of disabling UPDI to get a reset pin, none of them are as convenient a development cycle as we're used to. In most cases, the most convenient development configuration is to simply use UPDI programming, and leave any serial connection open while programming via UPDI using a programmer on a different port. Note that the 2-series 20 and 24 pin parts have enhancements that make a bootloader capable of providing a better developer experience possible.
- It takes 512b of flash - 1/4th or 1/8th of the total, but offers little, if any, advantages.
Buy official megaTinyCore breakouts and support continued development
ATtiny402 assembled ATtiny412/212/402/202 bare board