bq20z80-V101
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SLUS625D–SEPTEMBER 2004–REVISED OCTOBER 2005
Periodic AFE Verification
The bq20z80 periodically (DF:AFE Check Time) compares the entire RAM in the bq29312A with that of the
bq20z80 data flash and the expected control-bit states. If an error is detected, the internal AFE_Fail_Counter is
incremented. If the internal AFE_Fail_Counter reaches the DF:AFE Fail Limit, the bq20z80 reports a permanent
failure and SBS.PFStatus( ) [AFE_P] is set.
The internal AFE_Fail_Counter is decremented by one count each DF:AFE Fail Recovery Time.
However, if DF:Permanent Fail Cfg [XAFE_P] is set, the SAFE pin is driven low and the SAFE pin is driven high,
and if DF:AFE Check Time is set to 0, this feature is disabled.
SIZE
(BYTES)
DEFAULT
VALUE
NAME
CLASS / SUBCLASS
FORMAT
VALID RANGE
UNITS
AFE Check Time
2nd Level Safety / AFE Verification (20)
Integer
0 to 255
1
s
0 (10 typical)
Data Flash Failure
The bq20z80 can detect if the data flash is not operating correctly. DF:PF Flags 1 [DFF] is set when either (i))
After a full reset the instruction flash checksum does not verify, (ii) if any data flash write does not verify or (iii) if
any data flash erase does not verify.
If DF:Permanent Fail Cfg [XDFF] is set, the SAFE pin is driven low and the SAFE pin is driven high when DF:PF
Flags 1 [DFF] becomes set.
Fuse State Detection
The bq20z80 can detect if an attempt has been made to blow the fuse, but this has failed. If the bq20z80 DF:PF
Flag 1 is set and SBS.Current( ) is ≥ DF:Fuse Fail Limit in either charge or discharge directions for a period ≥
the DF:Fuse Fail Time, SBS.PFStatus( ) [FBF] is set.
When the DF:Fuse Fail Time timer begins, SBS.PFAlert( ) [FBF] is set. When the DF:Fuse Fail Time timer
expires or is cleared, SBS.PFAlert( ) [FBF] is cleared.
SIZE
(BYTES)
DEFAULT
VALUE
LABEL
CLASS / SUBCLASS
FORMAT
VALID RANGE
UNITS
Fuse Fail Time
Fuse Fail Limit
0 to 30
0 to 20
1
1
s
0 (10 typical)
2
2nd Level Safety /
Fuse Verification (21)
Integer
mA
24
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