The EVAL-ADAU1701MINIZ schematic shows that the DSP reset pin should be connected to the USBi interface board.
I've probed the reset trace (using a scope with falling edge trigger) and noticed that no matter what, the reset pin stays at logic high (not even when I've downloaded a program to the EEPROM)
The only time that RESET pin was triggered is when I manually set the device to disable (see picture)
My question is - is it really necessary to wire the RESET pin to the USBi plug? SigmaStudio can still operate without using this pin?
Thanks for your detailed response!
I agree that adding a single trace for REEST pin is not a big deal, but it's not all.
If the USBi board RESET output pin was an open-drain type, then everything…
Where I work we've made two -1701 products. One has three jumpers and a 10-pin header to bring all three signals (I2C clock, data, and reset) directly from an external USBi to the -1701, The other only has two jumpers for only the I2C signals. The USBi reset instead goes to an input on the product's PIC uC, with a PIC output to the -1701 reset. I don't have the code handy so I cannot say if this routinely transfers the reset. EDIT: The uC's C code does perform this transfer as part of its normal operation loop.
Perhaps no one has answered your question due to the risk of providing a wrong answer vs. just adding that trace from the USBi header to the -1701 reset pin. However, in addition to your experiments there is some evidence in the docs which suggests that your conclusion is correct. The first is this illustration in the Selfboot Application Note, AN923:
The second is the Core Control Register in the ADAU1701 Data Sheet (page 39), which provides core-stopping and register-clearing bits. This sounds like everything you need to load a new program into a warm -1701.
I was not able, however, to find one place definitely stating that the reset connection is unnecessary in all circumstances.
If the USBi board RESET output pin was an open-drain type, then everything could have been mush simpler.
But its not, it has a pull-up resistor:
Now, this can couse problems, because if the target board in off, and the USBi is still on, the RESET pin will inject 3.3V directly to the RESET pin while the IC is off...not a good idea.
And it's also works the other way around if the USBi board is off and the target board is on, due to the fact that the target board also has a pull-up resistor from RESET to VCC.
The solution is to add the 3-state buffer between two board, which will protect each other in power-off situations.
If the RESET pin is not necessary, I can also discard this protection buffer...