- why are pins 16 (VDD) and 24 (DVDD) unconnected?
- What the different voltage domains (VDDA, VDDD, VDD3P3, VDD_RTC, VDDPST and DVDD) are?
- The function of pin 6 (TOUT)?
- The function of pin 7 (XPD_DCDC)?
My educated guesses for the rails:
- VDDA/VDDD for analog and digital supply domains
- VDD_RTC a low-power rail that only powers an internal RTC (but there's no external 32kHz crystal)
- VDD3P3 an input rail for an internal LDO/DCDC converter
- VDDPST no idea, seems to be an I/O supply rail maybe
- DVDD and maybe VDD are perhaps outputs from the internal LDO
The pin XPD_DCDC is perhaps an enable line for some internal regulator.
edit 20140916: it appears that pin 16 and 24 are GPIO now (GPIO4 and 5, respectively), and that XPD_DCDC is a power down pin which may disable the transmitter (X=transmit) without requiring the chip to "reboot" when coming out of power down. TDO is also known as GPIO15 and determines master/slave boot mode.
It'd be *really* nice to get some information on the slave boot mode and whether you can communicate with the device via SPI instead of UART.