Datasheet

bq27541-G1

www.ti.com

SLUSAL6C –NOVEMBER 2011–REVISED OCTOBER 2012

Occasionally, a data flash CLASS will be larger than the 32-byte block size. In this case, the DataFlashBlock( )

command is used to designate which 32-byte block the desired locations reside in. The correct command

address is then given by 0x40 + offset modulo 32. For example, to access Terminate Voltage in the Gas

Gauging class, DataFlashClass( ) is issued 80 (0x50) to set the class. Because the offset is 67, it must reside in

the third 32-byte block. Hence, DataFlashBlock( ) is issued 0x02 to set the block offset, and the offset used to

index into the BlockData( ) memory area is 0x40 + 67 modulo 32 = 0x40 + 16 = 0x40 + 0x03 = 0x43.

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-G1 — 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 not resolve the fault.

MANUFACTURER INFORMATION BLOCKS

The bq27541-G1 contains 64 bytes of user programmable data flash storage: Manufacturer Info Block A and

Manufacturer Info Block B, . 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 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-G1 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 or 0x02 with this

command causes the corresponding information block (A or B 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.

ACCESS MODES

The bq27541-G1 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, , that are

accessible to the user. Manufacture Information refers to the two 32-byte blocks.

Table 6. Data Flash Access

SECURITY MODE DATA FLASH MANUFACTURER INFORMATION

FULL ACCESS R/W R/W

UNSEALED R/W R/W

SEALED None R (A); R/W (B)

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

bq27541-G1 to write access-mode transition keys stored in the Security class.

Product Folder Links: bq27541-G1