I just received a small proto run of boards and am attempting to boot.
Unfortunately, I cannot find the cause of XRESET pin remaining at 0.5V.
The design is stable, so this issue is a bit of a surprise. The major change is that we transitioned the RAM from 1Mb to 4Mb to improve SD card compatibility.
- XRESET pin static (DC) impedance to ground and IOVDD is same as known-good PCB. Pull-up resistor measures 100kΩ.
- 12.288MHz is not starting. Swapped all 12.288 components. Caps are 10pF, and parallel 1MΩ is present.
- XTALI and XTALO pins have an extremely brief pulse at boot or turn off, but never oscillation with 10pF oscope probe. Same 10x oscope probe sees 12.288MHz on known-good (prior version) board.
- 32kHz clock is oscillating
- IOVDD is 2.0V
- CVDD is 1.8V
- AVDD is 2.5V
- I've checked the many gpio pins that configure boot.
- D7 is pulled-high (we want 3V3)
- pwrbtn is high
- Vhigh is 5V
some references to somewhat related boot issues:
Pasi said for VS1000:
Not sure if this applies to VS1005GGPIO0_7 state is read immediately after the oscillator has started after power-on reset
Any ideas would be greatly appreciated!it needs proper clock and voltages to resume from reset