ds2782 Maxim Integrated Products, Inc., ds2782 Datasheet - Page 24

• Manufacturer Part Number: ds2782
• Description: Ds2782 Stand-alone Fuel Gauge Ic
• Manufacturer: Maxim Integrated Products, Inc.

Basic Transaction Formats
Write:
A write transaction transfers one or more data bytes to the DS2782. The data transfer begins at the memory
address supplied in the MAddr byte. Control of the SDA signal is retained by the master throughout the transaction,
except for the Acknowledge cycles.
Read:
A read transaction transfers one or more bytes from the DS2782. Read transactions are composed of two parts, a
write portion followed by a read portion, and is therefore inherently longer than a write transaction. The write portion
communicates the starting point for the read operation. The read portion follows immediately, beginning with a
Repeated START, Slave Address with R/W set to a 1. Control of SDA is assumed by the DS2782 beginning with
the Slave Address Acknowledge cycle. Control of the SDA signal is retained by the DS2782 throughout the
transaction, except for the Acknowledge cycles. The master indicates the end of a read transaction by responding
to the last byte it requires with a No Acknowledge. This signals the DS2782 that control of SDA is to remain with
the master following the Acknowledge clock.
Write Data Protocol
The write data protocol is used to write to register and shadow RAM data to the DS2782 starting at memory
address MAddr. Data0 represents the data written to MAddr, Data1 represents the data written to MAddr + 1 and
DataN represents the last data byte, written to MAddr + N. The master indicates the end of a write transaction by
sending a STOP or Repeated START after receiving the last acknowledge bit.
The msb of the data to be stored at address MAddr can be written immediately after the MAddr byte is
acknowledged. Because the address is automatically incremented after the least significant bit (lsb) of each byte is
received by the DS2782, the msb of the data at address MAddr + 1 is can be written immediately after the
acknowledgement of the data at address MAddr. If the bus master continues an auto-incremented write transaction
beyond address 4Fh, the DS2782 ignores the data. Data is also ignored on writes to read-only addresses and
reserved addresses, locked EEPROM blocks as well as a write that auto increments to the Function Command
register (address FEh). Incomplete bytes and bytes that are Not Acknowledged by the DS2782 are not written to
memory. As noted in the Memory Section, writes to unlocked EEPROM blocks modify the shadow RAM only.
Read Data Protocol
The Read Data protocol is used to read register and shadow RAM data from the DS2782 starting at memory
address specified by MAddr. Data0 represents the data byte in memory location MAddr, Data1 represents the data
from MAddr + 1 and DataN represents the last byte read by the master.
Data is returned beginning with the most significant bit (msb) of the data in MAddr. Because the address is
automatically incremented after the least significant bit (lsb) of each byte is returned, the msb of the data at
address MAddr + 1 is available to the host immediately after the acknowledgement of the data at address MAddr. If
the bus master continues to read beyond address FFh, the DS2782 outputs data values of FFh. Addresses labeled
“Reserved” in the memory map return undefined data. The bus master terminates the read transaction at any byte
boundary by issuing a No Acknowledge followed by a STOP or Repeated START.
Function Command Protocol
The Function Command protocol executes a device specific operation by writing one of the function command
values (FCmd) to memory address FEh. Table 5 lists the DS2782 FCmd values and describes the actions taken by
each. A one byte write protocol is used to transmit the function command, with the MAddr set to FEh and the data
S SAddr W A MAddr A Data0 A Data1 A … DataN A P
S SAddr W A MAddr A Sr SAddr R A Data0 A Data1 A … DataN N P
S SAddr W A MAddr A Data0 A P
S SAddr W A MAddr A Sr SAddr R A Data0 N P
Write Portion
Read Portion
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