I just purchased the ARM-USB-OCD-H to do some JTAG work using openocd. I have been reviewing the manual and although it confirms that the interface can operate with targets between 1.65V and 5V, I can't see anywhere where the manual states how to set the voltage of the target being probed. I found nothing in the openocd manual or the Olimex .cfg file. Obviously I don't want to be applying 5V logic to a device that oprates at 1.8V as that may damage the device.
Does anyone know how to ensure that the voltage of the target device is appropriately set? Or is there some auto-detection involved?
It is always 5V DC! There is no way to use the powering from ARM-USB-OCD-H for 3.3V or 1.8V targets without additional voltage divider to lower the 5V! The divider should lower the 5V to desired voltage suitable for the target! If it is a custom-made board you can probably place the voltage divider there, but you can also just skip pin #19 and power your target from another source or place.
Notice that powering of the target via the JTAG connector is just an extra. By default the JTAG standard doesn't specify this pin #19 for such powering function. You can leave pin #19 unconnected and power the board from another location.
Good that you asked.
Thank you for the reply. I already understood that the available DC supply voltage to the DUT is set at 5V only on the H variant. My question in particular was about the signal voltage levels on the bus. I am guessing here that one should connect the DUT VCC to VREF and this will govern the signal voltage level output from the ARM-USB-OCD-H, but this is not explicitly stated in the manual so I was looking for a confirmation. Sorry if my original question was not clear enough on that point.
Yes, there is probing on VREF, then, in the case of ARM-USB-OCD-H, sophisticated level adjustment for the rest of signals. It is done with active bi-directional converters.
Thank you for confirming that.