ARM-USB-TINY-H 1.8v jtag support?

[sophana]

Hi

Looking at FT2232h datasheet, it is written that VCC-IO should be 3.3v, but no minimal voltage value is given.
Does it mean that the dongle is not compatible with 1.8v jtag ports?

We tried ARM-USB-TINY-H with a 1.8v jtag port, and it seems to work.

My question is why does it work?
Is VCC-IO connected to jtag port power? or is VCC-IO connected to 3.3v?
Is it protection resistors that could make it "work"
My last question is that is it safe to use the dongle on a 1.8v jtag port without damaging the chip?

[LubOlimex]

For 1.8V targets it is not recommended to use ARM-USB-TINY-H. Consider ARM-USB-OCD-H which is suitable for targets powered by down to 1.65V.

Refer to table 1 on page 7 of the user manual:

https://www.olimex.com/Products/ARM/JTAG/_resources/ARM-USB-TINY_and_TINY_H_manual.pdf

Check the "Target voltage range" row.

It is also mentioned in the features and several places in the manual of ARM-USB-TINY-H:

"Supports ARM targets working in voltage range 2.0 – 5.0 V DC"

[sophana]

thanks for your response.
It seem they have the same chipset.
May I know what is the hardware difference that make ARM-USB-OCD-H compatible with lower voltage?
Is there any schematic somewhere?

[sophana]

Sorry. I think I just saw your response in a nother thread: https://www.olimex.com/forum/index.php?topic=6761.0
So ARM-USB-OCD-H has level shifters. correct?

[LubOlimex]

Both units have same FTDI chip which works down at 2V but ARM-USB-OCD-H design also incorporates SN74LVC2T45 voltage translators that allow reliable lower voltage operation (down to 1.65V).

The design is propriety and we don't share the schematic but we usually try to provide details if you need such.