BQ27500-V120 Datasheet, PDF (17/36 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

bq27500-V120
www.ti.com
System-Side Impedance Track™ Fuel Gauge
SLUS880 – OCTOBER 2008
None of the data written to memory are bounded by the bq27500– the values are not rejected by the fuel
gauge. Writing an incorrect value may result in hardware failure due to firmware program interpretation of
the invalid data. The written data is persistent, so a power-on reset does resolve the fault.
4.3 MANUFACTURER INFORMATION BLOCKS
The bq27500 contains 96 bytes of user programmable data flash storage: Manufacturer Info Block A,
Manufacturer Info Block B, Manufacturer Info Block C. The method for accessing these memory
locations is slightly different, depending on whether the device is in UNSEALED or SEALED modes.
When in UNSEALED mode and when and 0x00 has been written to BlockDataControl( ), accessing the
manufacturer information blocks is identical to accessing general data flash locations. First, a
DataFlashClass( ) command is used to set the subclass, then a DataFlashBlock( ) command sets the
offset for the first data flash address within the subclass. The BlockData( ) command codes contain the
referenced data flash data. When writing the data flash, a checksum is expected to be received by
BlockDataChecksum( ). Only when the checksum is received and verified is the data actually written to
data flash.
As an example, the data flash location for Manufacturer Info Block B is defined as having a Subclass =
58 and an Offset = 32 through 63 (32 byte block). The specification of Class = System Data is not needed
to address Manufacturer Info Block B, but is used instead for grouping purposes when viewing data
flash info in the bq27500 evaluation software.
When in SEALED mode or when 0x01 BlockDataControl( ) does not contain 0x00, data flash is no longer
available in the manner used in UNSEALED mode. Rather than issuing subclass information, a
designated manufacturer information block is selected with the DataFlashBlock( ) command. Issuing a
0x01, 0x02, or 0x03 with this command causes the corresponding information block (A, B, or C,
respectively) to be transferred to the command space 0x40…0x5f for editing or reading by the system.
Upon successful writing of checksum information to BlockDataChecksum( ), the modified block is returned
to data flash. Note: Manufacturer Info Block A is read-only when in SEALED mode.
4.4 ACCESS MODES
The bq27500 provides three security modes (FULL ACCESS, UNSEALED, and SEALED) that control
data flash access permissions, according to Table 4-6. Data Flash refers to those data flash locations,
specified in Table 4-7, that are accessible to the user. Manufacture Information refers to the three 32-byte
blocks.
Security Mode
FULL ACCESS
UNSEALED
SEALED
Table 4-6. Data Flash Access
Data Flash
R/W
R/W
None
Manufacture Information
R
R
R
Although FULL ACCESS and UNSEALED modes appear identical, only FULL ACCESS allows the
bq27500 to write access-mode transition keys.
4.5 SEALING/UNSEALING DATA FLASH
The bq27500 implements a key-access scheme to transition between SEALED, UNSEALED, and
FULL-ACCESS modes. Each transition requires that a unique set of two keys be sent to the bq27500 via
the Control( ) control command. The keys must be sent consecutively, with no other data being written to
the Control( ) register between them. Note that to avoid conflict, the keys must be different from the codes
presented in the CNTL DATA column of Table 4-2 Control( ) subcommands.
When in SEALED mode, the CONTROL_STATUS [SS] bit is set, but when the unseal keys are correctly
received by the bq27500, the [SS] bit is cleared. When the full-access keys are correctly received, then
the CONTROL_STATUS [FAS] bit is cleared.
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GENERAL DESCRIPTION
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