Jeff Smith

undocumented bits in ESTAT or FSTAT

Discussion created by Jeff Smith on Aug 25, 2006
Latest reply on Sep 14, 2006 by Jeff Smith
I've been experimenting with writing and verifying that EEPROM is blank (MCU is MC9S12DG128B). I've found two undocumented features.

1. In ESTAT, bit0 is always set where docs say it is clear. I have no clue why.

2. Bit1 seems to be the "EEPROM not blank" error flag, which is also not documented. The problem is that since nothing says there was such a flag, then who would know that this flag must be cleared before any further operation??

When I used cmd 0x05 to test for blank EEPROM, ESTAT became 0xc3. "Fine", I thought, because bit0 is always set and bit1 is just another way to tell that bit2 (BLANK) is not set. So I typed `mm 800 ff` so that D-Bug12 would clear the word that was programmed. Woops, that crashed D-Bug12, because even it did not know that 0x02 must be written to ESTAT first to clear the undocumented flag.

Does anyone know about this, or is it documented anywhere?