C8051F960-B-GM Datasheet, PDF (251/492 Pages) Silicon Laboratories – Ultra Low Power 128K, LCD MCU Family

C8051F96x
18.5.2. PSWE Maintenance
1. Reduce the number of places in code where the PSWE bit (b0 in PSCTL) is set to a 1. There should
be exactly one routine in code that sets PSWE to a 1 to write flash bytes and one routine in code that
sets both PSWE and PSEE both to a 1 to erase flash pages.
2. Minimize the number of variable accesses while PSWE is set to a 1. Handle pointer address updates
and loop maintenance outside the "PSWE = 1;... PSWE = 0;" area. Code examples showing this can
be found in “AN201: Writing to Flash from Firmware," available from the Silicon Laboratories web
site.
3. Disable interrupts prior to setting PSWE to a 1 and leave them disabled until after PSWE has been
reset to 0. Any interrupts posted during the flash write or erase operation will be serviced in priority
order after the flash operation has been completed and interrupts have been re-enabled by software.
4. Make certain that the flash write and erase pointer variables are not located in XRAM. See your
compiler documentation for instructions regarding how to explicitly locate variables in different
memory areas.
5. Add address bounds checking to the routines that write or erase flash memory to ensure that a
routine called with an illegal address does not result in modification of the flash.
18.5.3. System Clock
1. If operating from an external crystal, be advised that crystal performance is susceptible to electrical
interference and is sensitive to layout and to changes in temperature. If the system is operating in an
electrically noisy environment, use the internal oscillator or use an external CMOS clock.
2. If operating from the external oscillator, switch to the internal oscillator during flash write or erase
operations. The external oscillator can continue to run, and the CPU can switch back to the external
oscillator after the flash operation has completed.
Additional flash recommendations and example code can be found in “AN201: Writing to Flash from Firm-
ware," available from the Silicon Laboratories website.
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