Rainbow Electronics DS2781 - Manual (Page 20)

DS2781: Two-Cell Standalone Fuel Gauge IC
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EEPROM REGISTER
The EEPROM register provides access control of the EEPROM blocks. EEPROM blocks can be locked to prevent
alteration of data within the block. Locking a block disables write access to the block. Once a block is locked, it
cannot be unlocked. Read access to EEPROM blocks is unaffected by the lock/unlock status.
Figure 17. EEPROM REGISTER FORMAT
Address 1Fh Bit Definition
Field Bit Format Allowable Values
EEC 7 Read Only
EEPROM Copy Flag
Set to 1 when: Copy Data command executed
Cleared to 0 when: Copy Data command completes
Note: While EEC = 1, writes to EEPROM addresses are ignored
Power-up default: 0
LOCK 6
Read /
Write to 1
EEPROM Lock Enable
Host write to 1: Enables the Lock command. Host must issue Lock
command as next command after writing Lock Enable bit to 1.
Cleared to 0 when: Lock command completes or when Lock command
not the command issued immediately following the Write command
used to set the Lock Enable bit.
Power-up default: 0
Reserved 2:6 Undefined
BL1 1 Read Only
EEPROM Block 1 Lock Flag (Parameter EEPROM 60h–7Fh)
0: EEPROM is not locked
1: EEPROM block is locked
Factory default: 0
BL0 0 Read Only
EEPROM Block 0 Lock Flag (User EEPROM 20h–2Fh)
0: EEPROM is not locked
1: EEPROM block is locked
Factory default: 0
MEMORY
The DS2781 has a 256 byte linear memory space with registers for instrumentation, status, and control, as well as
EEPROM memory blocks to store parameters and user information. Byte addresses designated as “Reserved”
return undefined data when read. Reserved bytes should not be written. Several byte registers are paired into two-
byte registers in order to store 16-bit values. The most significant byte (MSB) of the 16 bit value is located at a
even address and the least significant byte (LSB) is located at the next address (odd) byte. When the MSB of a
two-byte register is read, the MSB and LSB are latched simultaneously and held for the duration of the read data
command to prevent updates to the LSB during the read. This ensures synchronization between the two register
bytes. For consistent results, always read the MSB and the LSB of a two-byte register during the same read data
command sequence.
EEPROM memory consists of the non-volatile EEPROM cells overlaid with volatile shadow RAM. The Read Data
and Write Data commands allow the 1-Wire interface to directly accesses only the shadow RAM. The Copy Data
and Recall Data function commands transfer data between the shadow RAM and the EEPROM cells. In order to
modify the data stored in the EEPROM cells, data must be written to the shadow RAM and then copied to the
EEPROM. In order to verify the data stored in the EEPROM cells, the EEPROM data must be recalled to the
shadow RAM and then read from the shadow RAM.