BQ27505 Datasheet, PDF (19/42 Pages) Texas Instruments – System-Side Impedance Track™ Fuel Gauge

Not Recommended for New Designs
bq27505
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SLUS884 – FEBRUARY 2009
4.1.2.7 DeviceNameLength( ): 0x62
UNSEALED and SEALED Access: This byte contains the length of the Device Name.
4.1.2.8 DeviceName( ): 0x63…0x69
UNSEALED and SEALED Access: This block contains the device name that is programmed in Device
Name.
4.1.2.9 ApplicationStatus( ): 0x6a
This byte function allows the system to read the bq27505 Application Status data flash location. See
Table 6-1 for specific bit definitions.
4.1.2.10 Reserved — 0x6b–0x7f
4.2 DATA FLASH INTERFACE
4.2.1 ACCESSING THE DATA FLASH
The bq27505 data flash is a non-volatile memory that contains bq27505 initialization, default, cell status,
calibration, configuration, and user information. The data flash can be accessed in several different ways,
depending on what mode the bq27505 is operating in and what data is being accessed.
Commonly accessed data flash memory locations, frequently read by a system, are conveniently
accessed through specific instructions, already described in Section 4.1, DATA COMMANDS . These
commands are available when the bq27505 is either in UNSEALED or SEALED modes.
Most data flash locations, however, are only accessible in UNSEALED mode by use of the bq27505
evaluation software or by data flash block transfers. These locations should be optimized and/or fixed
during the development and manufacture processes. They become part of a golden image file and can
then be written to multiple battery packs. Once established, the values generally remain unchanged during
end-equipment operation.
To access data flash locations individually, the block containing the desired data flash location(s) must be
transferred to the command register locations, where they can be read to the system or changed directly.
This is accomplished by sending the set-up command BlockDataControl( ) (0x61) with data 0x00. Up to 32
bytes of data can be read directly from the BlockData( ) (0x40…0x5f), externally altered, then rewritten to
the BlockData( ) command space. Alternatively, specific locations can be read, altered, and rewritten if
their corresponding offsets are used to index into the BlockData( ) command space. Finally, the data
residing in the command space is transferred to data flash, once the correct checksum for the whole block
is written to BlockDataChecksum( ) (0x60).
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 48, it must reside in the second 32-byte block. Hence, DataFlashBlock( ) is issued 0x01 to set the
block offset, and the offset used to index into the BlockData( ) memory area is 0x40 + 48 modulo 32 =
0x40 + 16 = 0x40 + 0x10 = 0x50.
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 bq27505 – 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.
Copyright © 2009, Texas Instruments Incorporated
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GENERAL DESCRIPTION
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