8.5.4.1 Accessing the Data Flash

The bq27545-G1 data flash is a non-volatile memory that contains initialization, default, cell status, calibration, configuration, and user information. The data flash can be accessed in several different ways, depending on what mode the bq27545-G1 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 Data Commands. These commands are available when the bq27545-G1 is either in UNSEALED or SEALED modes.

Most data flash locations, however, are only accessible in UNSEALED mode by use of the bq27545-G1 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 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 bq27545-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.