ATtiny 204/404/804/1604

Specifications	ATtiny204	ATtiny404	ATtiny804	ATtiny1604
Flash (program memory)	2048 bytes	4096 bytes	8192 bytes	16384 bytes
Flash w/Optiboot	1536 bytes	3584 bytes	7680 bytes	15872 bytes
RAM	128 bytes	256 bytes	512 bytes	1024 bytes
EEPROM	64 bytes	128 bytes	128 bytes	256 bytes
Bootloader(optional)	Optiboot (No! Don't waste a quarter of the flash!)	Optiboot (strongly not recommended due to size)	Optiboot (awkward but viable, not recommended)	Optiboot (awkward but viable, not recommended)
GPIO Pins	12 (11 usable)	12 (11 usable)	12 (11 usable)	12 (11 usable)
ADC Channels	10 (9 usable)	10 (9 usable)	10 (9 usable)	10 (9 usable)
DAC	No	No	No	No
PWM Channels	6	6	6	6
Timer Type B	1	1	1	1
Timer Type D	No	No	No	No
CCL Logic Blocks	2 (no int)	2 (no int)	2 (no int)	2 (no int)
Event Channels	3, 1 sync 2 async	3, 1 sync 2 async	3, 1 sync 2 async	3, 1 sync 2 async
Interfaces	UART, SPI, I2C	UART, SPI, I2C	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, expected to be fine @ 5v and room temperature.
25	Internal, tuned	OVERCLOCKED, expected to be fine @ 5v and room temperature.
30	Internal, tuned	OVERCLOCKED, may be unstable.
24	External Clock	OVERCLOCKED, expected to be fine @ 5v and room temperature. Uses CLKI/PA3 as above.
25	External Clock	OVERCLOCKED, expected to be 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.

External crystal

These parts support an external 32.768 kHz crystal clock source for the RTC. Conveniently, the pins for this are... PB2 and PB3, the same pins used by default for the USART. These parts expect a crystal with a very low load capacitance, on the order of 6pf. A pair of loading capacitors of a few pF each is necessary for it to oscillate, and traces between chip and crystal must be kept very short. There is rarely a need to use it. At room temperature and 3-5V, the internal oscillator and oscillator error stored in the SIGROW can be used to calculate the clock speed of the (inaccurate, but stable) 32 kHz internal RTC oscillator accurately enough to use it to tune the chip as described above, a sketch for this will be provided with a future version of this core.

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, 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 an alternate reset pin feature which makes a better developer experience possible with a bootloader.

On parts with less than 8k, in addition to the woes surrounding bootloader entry, the 512b of flash the bootloader requires is no longer negligible.

Buy official megaTinyCore breakouts and support continued development

ATtiny1604 assembled - while supplies last only. We are discontinuing all 0-series assembled boards.

ATtiny3224/1624/824/424/1614/814/414/214/1604/804/404/204 bare board

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