Is it possible to have the state of an output driver change from just before a BOD is detected to just after the reset occurs.
I have a gpio controlling a power booster. This booster charges an output capacitor which drives 3.3 volt power on the board, which drives the VDD pins (VDDS,VDDS2,VDDS_DCDC and ultimately VDDR,VDDR_RF as well) on the CC2640 chip. I'm attempting to put the board into a power cycle, whereby the power booster is first turned on, allowing the booster output capacitor to charge up to 3.3 volts. The power booster is then turned off, immediately followed by putting the cc2640 into shutdown. My hope is it takes many seconds for the capacitor to drain to the point where the BOD triggers and the cc2640 is reset.
I have this circuit implemented and it behaves as indicated...the voltage on the output cap (VDD_3_3) goes to 3.3 volt almost immediately after the power booster is turned on. Then when the power booster is turned off and the cc2640 is shut down, the voltage slowly trickles down to 1.65 (or there abouts). The BOD event seems to trigger, because the power booster seems to be turned on for a brief period. The voltage goes up immediately, but not to the expected voltage of 3.3 volt. It only goes up to about 1.9 volts and then proceeds to trickle down again to 1.65. It then is stuck in a cycle up to 1.9 then trickles down to 1.65.
I attached my scope to the resetn pin on the cc2640, attempting to see a reset pulse, but I can't trigger on one. If it is occurring, it is so fast, my 50 Mhz oscilloscope is not catching it. I thought I should see a 100 ns or wider pulse on the resetn pin when the BOD event occurs. But I don't see it. I thought the resetn pin could be used as an output to drive reset on my board. I don't currently send this signal to anything other than a 100 kohm resistor tied to VDD_3_3 and a 100 nF capacitor to ground. This is the same resetn circuit shown on the 2650EM-7ID_1_2_6_Schematic.pdf, which TI supplied.
I was hoping the gpio outputs would be tri-stated long enough for a pull-down of 10 Mohm to drive a signal low, which would turn on the power booster. But I also thought I might need the gpio to be tri-stated during the time the script runs after a resetn event. It seems like the chip never begins executing from the BOD resetn event. It's as if the BOD does not cause a valid reset of the chip.
In order to implement this, I need the state of the gpio pin to transition when the BOD triggers.
Is it possible to write a value to a latch or register in the CC2640 which causes the state of the gpio pin to change after the BOD event causes a reset?
I see a documentation describing how the state of the gpio's is maintained when transitioning from shutdown to active, however, there doesn't seem to be an adequate description of what happens to the gpios across a BOD reset event.
John
