Hi, all. The 5223X has the ability to detect when the supply voltage is dropping and force an interrupt. According to table 2.3 of the MCF52235 Data Sheet (still labeled "advance information" in revision 6!), the low voltage detect trip voltage is between 2.15 and 2.3 Volts.
I'd like to be able to save a few values in a block of internal flash between the time the low voltage interrupt occurs and power drops to a level that no longer permits reliable writing to flash. Has anyone an idea if this is possible? I.e., is it even possible to write to the internal flash at 2.15 Volts. If so, how much time does it take to write one block of flash, and how long after the interrupt occurs will power still be above whatever is required to write flash?
Assume the worst case, i.e., that power fails completely while the 5223X is in its full power mode, and assume that power capacitors and resistors are as recommended by Freescale, e.g., on their demo board or Figure 5. "Suggested Connection Scheme for Power and Ground" of the MCF52235 Data Sheet.
I guess that the first thing to do after receiving the interrupt would be to clear the Peripheral Power Management Registers (PPMRH, PPMRL) to shut down all the clocks and set all ports to be GPIO with their DDRs set to 0 (inputs) so the CPU wouldn't be sourcing more power than necessary...or is there a better way to do reduce power and still be able to write to the internal flash?
Thanks for whatever thoughts and information you may have.
- Richard
