BQ27541 Datasheet, PDF(18/38 Page) Texas Instruments – Single Cell Li-Ion Battery Fuel Gauge for Battery Pack Integration

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bq27541

SLUS861 â DECEMBER 2008 ........................................................................................................................................................................................... www.ti.com

Reading and writing subclass data are block operations up to 32 bytes in length. If during a write the data length

exceeds the maximum block size, then the data is ignored.

None of the data written to memory are bounded by the bq27541 â 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.

MANUFACTURER INFORMATION BLOCKS

The bq27541 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

bq27541 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 0x40â¦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.

ACCESS MODES

The bq27541 provides three security modes (FULL ACCESS, UNSEALED, and SEALED) that control data flash

access permissions according to Table 6. Data Flash refers to those data flash locations, specified in Table 7,

that are accessible to the user. Manufacture Information refers to the three 32-byte blocks.

Security Mode

FULL ACCESS

UNSEALED

SEALED

Table 6. Data Flash Access

Data Flash

R/W

None

Manufacturer Information

R/W

R (A); R/W (B,C)

Although FULL ACCESS and UNSEALED modes appear identical, only FULL ACCESS mode allows the

bq27541 to write access-mode transition keys.

SEALING/UNSEALING DATA FLASH

The bq27541 implements a key-access scheme to transition between SELAED, UNSEALED, and

FULL-ACCESS modes. Each transition requires that a unique set of two keys be sent to the bq27541 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 2subcommands.

When in SEALED mode the [SS] bit of CONTROL_STATUS is set, but when the UNSEAL keys are correctly

received by the bq27541, 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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