This is an Open Source Hardware board based around the FTDI FT2232H chip to provide breakouts, buffering, and level conversion for a number of common embedded hardware interfaces. At present, this includes:
- SPI
- I2C
- JTAG
- SWD
- UART
It's intended to be easy to use and work with open source software, including tools like OpenOCD and Flashrom.
The hardware has dedicated headers for a variety of electrical interfaces. Connect the desired interface to you target. The pinout for SPI, I2C and UART are printed on the board, SWD follows the ARM SWD standard, and JTAG is the ARM 20 pin JTAG interface. (Electrically, however, it should work with most any processor supporting JTAG.)
You may only use one of the SPI, I2C, SWD, and JTAG interfaces at any given time. The UART is handled by dedicated pins in the FT2232H, so can be used simultaneously with one of the other interfaces.
There are 3 switches on the board. The mode switch selects how the reference power (for the interface) and the target are connected:
- Isolated: The interface is powered by the on-board voltage regulators, and the target must be powered by its own power supplies. The power rails are not connected to one another. You will almost always want to use this mode.
- Bridged: The interface is powered by the on-board voltage regulators which will also supply power to the target. The target must not be separately powered. This mode is useful for e.g., programming SPI/I2C flash out of circuit, or powering very small circuits -- maximum stable load is around 200mA.
- Target: The interface is partially powered from the target. (Specifically, the reference voltage for the level shifters.) In theory, this can be used for cases where the target voltage is not 5v, 3.3v, or 1.8v. The target voltage must still remain under 5V!
Note that the ground of your computer is connected to the ground of your target when you connect with this. In almost all cases, this is not a problem, but if both are powered via the wall ("mains"), there is a risk of noise due to ground loops, etc.
The voltage switch allows you to select the I/O voltage used in Isolated or
Bridged mode. It does nothing (well, except change an LED) in Target mode.
5V is supplied directly from the USB input, and there are onboard regulators
for 3.3v and 1.8v.
The remaining switch selects between JTAG/SPI and I2C/SWD. I2C and SWD use a bidirectional data line, so require special handling.
I've tested the board with OpenOCD for JTAG/SWD use and flashrom for SPI/I2C
flash. I'm planning to make a demo target board with a handful of interfaces on
it and provide that here in the future.
With OpenOCD, use the configuration file in configs. You will also need a
target configuration. Time permitting, I will post a tutorial on the use of
TIMEP and OpenOCD to debug targets.
With flashrom:
flashrom -p ft2232_spi:type=2232H,port=B,divisor=4
Use of port=B is critical, port A is wired to the UART, so will not work as
you intend. :)
Some efforts have been made to protect against mistakes that will destroy your hardware, but there is still some risk in using this if connected improperly.
Included protection in current revision:
- Current limiting resistors on I/O lines.
- 5v+ tolerant I/O.
- Warnings in the README. :)
Shorting power to ground may damage the target, the TIMEP interface, or the USB port on your computer (if running in 5V mode). This is unlikely, but be careful with your connections.
Using the wrong voltage may damage components not rated for that voltage. Any voltage up to 5v is tolerated on the interface board I/O pins, but beyond that may result in damage.
Additional protection that could be considered:
- Polyfuses on power/ground rails to computer.
- Clamping diodes on USB lines.
- Clamping diodes on I/O lines.
These have not been added because I have been trying to keep BOM cost down to get these in the hands of as many hardware hackers as possible.
Copyright 2020 Google, LLC
Maintainer: David Tomaschik david@systemoverlord.com
Please see CONTRIBUTORS.md for credit to all contributors.
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at
https://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
This is not an officially supported Google product.