BQ27500 Datasheet, PDF (17/39 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

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bq27500
bq27501
System-Side Impedance Track™ Fuel Gauge
SLUS785 – SEPTEMBER 2007
4.3 MANUFACTURER INFORMATION BLOCKS
The bq27350 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 Info 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 bq27500/1 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 bq27500/1 provides three security modes in which control data flash access permissions according to
Table 4-6. Public Access refers to those data flash locations, specified in Table 4-7, that are accessible to
the user. Private Access refers to reserved data flash locations used by the bq27500/1 system. Care
should be taken to avoid writing to Private data flash locations when performing block writes in FULL
ACCESS mode, by following the procedure outlined in Section 4.2.1.
Security Mode
BOOTROM
FULL ACCESS
UNSEALED
SEALED
Table 4-6. Data Flash Access
DF – Public Access
N/A
R/W
R/W
R
DF – Private Access
N/A
R/W
R/W
N/A
Although FULL ACCESS and UNSEALED modes appear identical, FULL ACCESS allows the bq27500/1
to directly transition to BOOTROM mode and also write access mode transition keys. The UNSEAL mode
lacks these abilities.
4.5 SEALING/UNSEALING DATA FLASH
The bq27500/1 implements a key-access scheme to transition between SEALED, UNSEALED, and
FULL-ACCESS modes. Each transition requires that a unique set of 2 keys be sent to the bq27500/1 via
the Control( ) control command. The keys must be sent consecutively, with no other data being written to
the Control( ) register in between. 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( )’s [SS] bit is set, but when the UNSEAL keys are correctly
received by the bq27500/1, 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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