[Oberon] FPGA - Voltage Convertor
paulreed at paddedcell.com
Fri Nov 27 18:17:48 CET 2020
> Just discovered this convertor, it is Arduino breed.
> Wondering how could be used with FPGA, what should connect where?
It seems (without having more information to confirm) that this is a
MOSFET-based bidirectional level convertor like this one from Adafruit:
It is designed for level-converting open-collector-style busses like
I2C, but can, with limitations, be used for a variety of applications.
The Adafruit page refers to the application notes from Philips/NXP which
explain its operation, which I think is quite elegant and they are well
worth a read.
I have used this type of converter on PS/2 signals (pulled up to 5V)
which need to be fed into and from a 3.3V or a 2.5V I/O bank on an FPGA.
In that case with this board, I'd probably connect HV to 5V and LV to
3.3V/2.5V, and then the corresponding LV1..LV4 signals to the FPGA, and
the HV1..HV4 to the corresponding PS/2 clock and data lines. But I'd
want a schematic of the board to be sure.
Note that the circuit is so simple it doesn't even need a ground (0V)
connection. That's because its bidirectional function is really: if
grounded on one side, bring the other side to ground.
This is different from the series resistor level-convertor on the
Digilent Spartan 3 PS/2 connector, which relies on the clamp diodes
inside the FPGA to keep the low-voltage level on the FPGA side. Not all
FPGAs are the same here, hence the MOSFET approach is safer (and the
MOSFET will probably blow up before the FPGA, providing some crude
More information about the Oberon