Understanding S5 switch on ADAU1701-MINIZ
Dear friends!
I'm quite new to the ADAU family of devices, so probably I'm going to ask some long-before-answered questions just due to lack of skills in web search, but, sorry, here it goes anyway)
While developing my design I'm wondering about the S5 switch on the ADAU1701-MINIZ evaluation board, eh, well) what's it for anyway?))) At first glance we need to set it in "down" position (towards the USBi connector) to set the WP pin low and enable writing to the EEPROM, but we need to set it high to allow the ADAU to self-boot. According to the datasheet at least. The page 27 of the datasheet says:
The ADAU1701 does not self-boot if WP is set low. Holding this pin low allows the EEPROM to be programmed in-circuit. The WP pin is pulled low (it typically has a resistor pull-up) to enable writes to the EEPROM, but this in turn disables the self-boot function until the WP pin is returned high.
But then I just left the switch in the down position and continued with programming and rebooting the board, and almost forgot that it's there, and it was (and still is) self-booting OK! Well, then I got back to my own schematics and... stumbled upon a question whether this switch is needed at all) So is it true that ADAU1701 (and ADAU1401A, which I am planning to use) is going to self-boot whatever the initial WP pin setting is?
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Great, thank you very much. The explanation why the write-protection of the EEPROM is important in JGAnguita 's thread. That's what didn't occur to me. Thanks again.
Hello Ivan,
You are correct, regardless of the switch position it will still boot. But to program the EEPROM, the switch must be in the up position (closest to the USBi connector).
I think what is happening is when the S5 switch connects the EEPROM to ground, this allows the device to be programmed, but the (disconnected) WP/CLATCH pin on the ADAU1701 is still pulled high, allowing it to self boot. During this time the EEPROM could still be modified (but it will never happen since the ADAU1701 does not try to write to it under normal operation).
When the switch is connected in down position, the ADAU1701's WP/CLATCH pin is again pulled high and will self boot itself out of power-up. The processor will pull the the WP pin low when programming the EEPROM from SigmaStudio. So other than when the EEPROM is accessed by the ADAU1701, it is protected due to the pullup.
So it seems the S5 switches only purpose is to allow the EEPROM device to be programmed.
The following thread provides some good insight on this: Re: Problem with self-booting in ADAU1701
-JT
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