EVAL-ADAU1772Z and BRD_/RESET (or BRD_RESET)
I am confused by the board reset signal used in the ADAU-1772Z and EVAL-ADUSB2EBZ.
In the ADAU-1772Z it is labeled BRD_RESET at S7 near the Stereo Output Jack J23 and also the EN pin of U4 LDO. Looks like this should be "BRD_/RESET".
The EVAL-ADAUSBEBZ however has the term BRD_/RESET on pin 8 of J1 Control cable as well as drawn as an output on page 8 of AN-1006 (is it an input or output?).
Please review and explain how the signal should be used and when.
hardware
adau1772
eval-adusb2ebz
Integrated/Special Purpose A/D Converters
Audio CODECs
Hello bkline,
BRD_RESET is a logic signal that appears in pretty much all of our eval boards with DSPs on them. This is a logic line that will be pulled up somewhere in the design. In this case it is R25 which is a 10K. So it is a weak pull up. It will keep the regulator enabled and turned on. There is a timing cap C29 to allow time for the incoming power to be stable before enabling the LDO.
OK, so now anything can pull this down and it will shut off the power and thereby reset the DSP. The Power/Bypass switch will pull this down to ground and shut off the LDO.
Then we also connect this to pin 6 of the USBi connector. ( You had this as pin 8 but it is pin 6)
This "output" from the USBi is actually an open collector logic line. It can pull down the logic line to ground or let it float. So it is not exactly an output, the pin will either be grounded or floating. Therefore technically it is an output.
So nothing is driving this BRD_RESET signal high, it is only pulled high so anything can pull it down. On many of our eval boards we have a reset button and also a reset generator but this design is simpler.
This means the USBi has the ability to reset the entire eval board. I have found this handy when I have placed entire eval boards into an environmental oven and needed to be able to reset the DSP.
You do it via SigmaStudio. Right click on the USBi GUI in the Config window.
Device Enable/Disable is what you select to pull down this logic line or to release it.
The only thing I do not like about this is that there is no feedback of the current state. There is no checkmark that will appear.
So be careful to not flip this too many times and forget the current state.
The RESET USB Interface, is NOT this signal, that only resets the Cirrus part on the USBi itself.
By the way, the Device Power ON/OFF is the 5V that the USBi can supply. This can be handy as well. You can do things like put in some transistors to translate this to do things like change the Selfboot pin or to power down some regulators on your board.
I suggest you use reset generators and wire up this BRD_RESET signal so that you can reset the USBi manually from the computer. The USBi never uses this when programming the DSPs.
Dave T
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