We are using our FS6500 (exactly MC33FS6520CAE) SBC for our automotive project.
IO and CAN wake-up sources can be configurable and working as we expect, but we cannot set "LONG_DURATION_TIMER" register by SPI. I mean all register can be changed by our SPI commands (incl. INIT_VREG, INIT_WU and LDT_AFTER_RUN, LDT_WAKE_UP and other registers too), but when we try to write 0x66 to register #6, it stays 0x04.
If we try to modify it in INIT state, we get SPI_REQ error as it have to be, but when we try to write it in NORMAL state, we do not get any error back. After that (when we read the value back) it stays 0x04 in all cases. We tried Function1, Function2, Function4 with configured 10-20-32 seconds, but when Function1 or 2 is selected, the counter does not starts to count and the SBC never enters to LPOFF. When Function4 is selected and we set SBC to LPOFF mode, 5V output switches off, but never wakes up (only after power cycle).
We tried to set LDT_WAKE_UP_1 to 10 and others are 0 and set LDT_WAKE_UP_3 to 10 and others to 0 too.
We are using this IC in our other project, but the circuit differs (both are made by our partners).
Thank you for your support.
FS6520 and FS6502 has different functions, LDT is available only in FS6502. Unfortunately only LONG_DURATION_TIMER register is not working, LDT_AFTER_RUN and LDT_WAKE_UP registers are seems to be working. I recommend to modify SPI responses for these registers to "ERROR, invalid request" or at least counter registers should not work too.
I try it in FRDMFS6523CAEVM EVB deubg mode,after enter normal mode this EVB write/read LONG_DURATION_TIMER register successfully, you can get detail information from below.
I test about write and read register-LONG_DURATION_TIMER in EVB,all test result shows no issue,I can write and read it successfully in normal mode and it only be modified under normal mode.
For your case please double check you send the correct SPI command especially following for the SPI timing,please refer to datasheet page22 figure9.
For the hardware please refer to attached KTFS4500-FS6500UG file.