Summary

• Write and read flash and EEPROM on UPDI-talking ATtiny and ATmega chips
• 12V enable pulse for High-Voltage programming
• Secondary serial port for debugging or console use
• Optional 6-pin 30cm programming cable
• Boxed header to ensure cable is oriented correctly
• Second UART also available on UPDI+ connector
• Compatibility with AVR DA chips
• New choice of USB A plug or micro B socket

What is it?

This adapter allows writing firmware to an AVR microcontroller that uses UPDI, such as the new 0-series and 1-series ATtiny, or 0-series ATmega chips. It uses a USB-UART chip, using the one-wire scheme, which connects RX directly to the target UPDI, and TX via a 4.7k resistor.

A switch allows an optional 12V enable pulse to be sent to the UPDI pin, allowing programming even while the pin is in RESET or GPIO mode. This pulse is sent entirely by hardware, as a result of the RTS handshaking line being asserted when the serial port is opened, and thus does not require any special support in the programming software on the PC.

Additionally, this programmer also provides a second serial port which is made accessible via the standard FTDI-like header pinout providing the TX/RX data pair and also the RTS/CTS handshaking lines. This port could be useful to connect to a debugging console on the target, or for other communications with it.

The secondary UART's TX and RX pins are also made available on two spare pins of the UPDI pin header. This is an extension of the original Atmel-specified UPDI connector, known here as UPDI+. The pinout is shared by other UPDI devices in the Maker community, such as MicroUPDI Programmer. The RX line is attached directly, while the TX line is supplied via a logic gate controlled by the DTR handshaking line. When DTR is asserted, the TX pin will transmit. When not asserted, the TX pin on the UPDI+ connector will be left at hiZ state. This means it won't interfere with the circuit if that pin is being used for other things than UART.

The two ports are provided by a single CP2105 USB-UART bridge chip, and so they will always enumerate over USB in the same order - the first (usually ttyUSB0 on Linux) will be the UPDI port, and the second (ttyUSB1) will be the debug/console serial port.

Both the programming (UPDI) and secondary UART IO pins on the front are direct feeds from the CP2105 chip, which uses 3.6V signalling. That’s a convenient voltage level just high enough to meet the requirements of a TTL chip running at 5V (they need at least 70% of VCC, i.e. 3.5V), while not being too high as to upset any chip running at 3.3V, because the overvoltage (of 0.3V) is not yet enough to forward-bias any protection diodes on the gates. In practice this means it should be fine talking to either 5V or 3.3V-powered AVR chips.

How to use it

In order to use this programmer you will need to use one of the following tools for actually writing firmware files to AVR chips:

• Device::AVR::UPDI
• pyupdi

For example, if you install the first one that will give you a new command, avr-updi. You can write an ATtiny814 chip from a file called firmware.hex with the command

$ avr-updi write-flash -p t814 firmware.hex

Why did you make it?

I needed a programmer like this for developing on the smaller ATtiny chips with 12V mode enabled.

What makes it special?

Besides this and my other cable, there don't appear to be any maker-oriented UPDI programming products. This programmer allows easy use of UPDI to write firmware onto AVR chips. The 12V mode is especially useful for freeing up one extra IO pin on the smaller ATtiny 1-series chips by switching the PA0 pin away from UPDI mode. The additional second serial port is also very handy for allowing both programming and serial console access from a single device, occupying only one USB port from the development computer. Including this secondary port also on the UPDI+ connector makes for a convenient single-cable connection with a supported target board.

Related Products

• AVR UPDI Programming Cable A simpler USB UPDI Programming which does not have the second serial port or 12V pulse generator

• ATtiny3217 Development Board A development board using the ATtiny3217 microcontroller

• ATtiny814 Development Board A development board using the ATtiny814 microcontroller