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DS2760BE+025

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P25
DS2760
13
EEPROM REGISTER
The format of the EEPROM Register is shown in Figure 11. The function of each bit is described in
detail in the following paragraphs.
EEPROM REGISTER FORMAT Figure 11
Address 07
b
it 7
b
it 6
b
it 5
b
it 4
b
it 3
b
it 2
b
it 1
b
it 0
EEC LOCK X X X X BL1 BL0
EEC – EEPROM Copy Flag. A 1 in this read-only bit indicates that a Copy Data command is in
progress. While this bit is high, writes to EEPROM addresses are ignored. A 0 in this bit indicates that
data may be written to unlocked EEPROM blocks.
LOCK – EEPROM Lock Enable. When this bit is 0, the Lock command is ignored. Writing a 1 to this
bit enables the Lock command. After the Lock command is executed, the LOCK bit is reset to 0. The
factory default is 0.
BL1 – EEPROM Block 1 Lock Flag. A 1 in this read-only bit indicates that EEPROM Block 1
(addresses 30-3F) is locked (read-only) while a 0 indicates Block 1 is unlocked (read/write).
BL0 – EEPROM Block 0 Lock Flag. A 1 in this read-only bit indicates that EEPROM Block 0
(addresses 20-2F) is locked (read-only) while a 0 indicates Block 0 is unlocked (read/write).
X – Reserved bits.
SPECIAL FEATURE REGISTER
The format of the Special Feature Register is shown in Figure 12. The function of each bit is described in
detail in the following paragraphs.
SPECIAL FEATURE REGISTER FORMAT Figure 12
Address 08
b
it 7
b
it 6
b
it 5
b
it 4
b
it 3
b
it 2
b
it 1
b
it 0
PS
PIO MSTR X X X X X
PS – PS Pin Mirror. This read-only bit mirrors the state of the PS pin. The reading of a 0 in this bit
should be immediately followed by writing a 1 to this location to insure proper operation.
PIO – PIO Pin Sense and Control. See the Programmable I/O section for details on this read/write bit.
MSTR - SWAP Master Status Bit. This bit indicates whether a device has been selected through the
SWAP command. Selection of this device through the SWAP command and the appropriate Net Address
will result in setting this bit, indicating that this device is the master. A 0 signifies that this device is not
the master.
X – Reserved bits.
DS2760
14
1-WIRE BUS SYSTEM
The 1-Wire bus is a system which has a single bus master and one or more slaves. A multidrop bus is a
1-Wire bus with multiple slaves. A single-drop bus has only one slave device. In all instances, the
DS2760 is a slave device. The bus master is typically a microprocessor in the host system. The
discussion of this bus system consists of four topics: 64-Bit Net Address, Hardware Configuration,
Transaction Sequence, and 1-Wire Signaling.
64-BIT NET ADDRESS
Each DS2760 has a unique, factory-programmed 1-Wire net address which is 64 bits in length. The first
8 bits are the 1-Wire family code (30h for DS2760). The next 48 bits are a unique serial number. The
last 8 bits are a CRC of the first 56 bits (see Figure 13). The 64-bit net address and the 1-Wire I/O
circuitry built into the device enable the DS2760 to communicate via the 1-Wire protocol detailed in the
1-Wire Bus System section of this data sheet.
1-WIRE NET ADDRESS FORMAT Figure 13
8-bit CRC 48-bit Serial Number 8-Bit Family Code 30h)
MSb LSb
CRC GENERATION
The DS2760 has an 8-bit CRC stored in the most significant byte of its 1-Wire net address. To ensure
error-free transmission of the address, the host system can compute a CRC value from the first 56 bits of
the address and compare it to the CRC from the DS2760. The host system is responsible for verifying the
CRC value and taking action as a result. The DS2760 does not compare CRC values and does not
prevent a command sequence from proceeding as a result of a CRC mismatch. Proper use of the CRC
can result in a communication channel with a very high level of integrity.
The CRC can be generated by the host using a circuit consisting of a shift register and XOR gates as
shown in Figure 10, or it can be generated in software. Additional information about the Dallas 1-Wire
Cyclic Redundancy Check is available in Application Note 27 entitled “
Understanding and Using Cyclic
Redundancy Checks with Dallas Semiconductor Touch Memory Products”. (This application note can be
found on the Maxim/Dallas Semiconductor website at www.maxim-ic.com).
In the circuit in Figure 14, the shift register bits are initialized to 0. Then, starting with the least
significant bit of the family code, one bit at a time is shifted in. After the 8
th
bit of the family code has
been entered, then the serial number is entered. After the 48
th
bit of the serial number has been entered,
the shift register contains the CRC value.
DS2760
15
1-WIRE CRC GENERATION BLOCK DIAGRAM Figure 14
HARDWARE CONFIGURATION
Because the 1-Wire bus has only a single line, it is important that each device on the bus be able to drive
it at the appropriate time. To facilitate this, each device attached to the 1-Wire bus must connect to the
bus with open-drain or tri-state output drivers. The DS2760 used an open-drain output driver as part of
the bidirectional interface circuitry shown in Figure 15. If a bidirectional pin is not available on the bus
master, separate output and input pins can be tied together.
The 1-Wire bus must have a pull-up resistor at the bus-master end of the bus. For short line lengths, the
value of this resistor should be approximately 5k
W. The idle state for the 1-Wire bus is high. If, for any
reason, a bus transaction must be suspended, the bus MUST be left in the idle state in order to properly
resume the transaction later. If the bus is left low for more than 120
ms, slave devices on the bus begin to
interpret the low period as a Reset Pulse, effectively terminating the transaction.
1-WIRE BUS INTERFACE CIRCUITRY Figure 15
TRANSACTION SEQUENCE
The protocol for accessing the DS2760 via the 1-Wire port is as follows:
§ Initialization
§ Net Address Command
§ Function Command
§ Transaction/Data
The sections that follow describe each of these steps in detail.
1mA
Typ.
100
W
MOSFET
Tx
Rx Rx
Tx
Rx = Receive
Tx = Transmit
+V
PULLUP
(2.0V–5.5V)
4.7kW
BUS MASTER DS2760 1-WIRE PORT
MSb
XOR
XOR
LSb
XOR
in
p
ut
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P25

DS2760BE+025

Mfr. #:
Buy DS2760BE+025
Manufacturer:
Maxim Integrated
Description:
Battery Management
Lifecycle:
New from this manufacturer.
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