DS2438 Dallas Semiconducotr, DS2438 Datasheet - Page 17

• Manufacturer Part Number: DS2438
• Description: Smart Battery Monitor
• Manufacturer: Dallas Semiconducotr

1-Wire BUS SYSTEM
The 1-Wire bus is a system which has a single bus master and one or more slaves. The DS2438 behaves
as a slave. The discussion of this bus system is broken down into three topics: hardware configuration,
transaction sequence, and 1-Wire signaling (signal types and timing).
HARDWARE CONFIGURATION
The 1-Wire bus has only a single line by definition; 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 have open
drain or 3-state outputs. The 1-Wire port of the DS2438 (DQ pin) is open drain with an internal circuit
equivalent to that shown in Figure 8. A multidrop bus consists of a 1-Wire bus with multiple slaves
attached. The 1-Wire bus requires a pull-up resistor of approximately 5 k .
HARDWARE CONFIGURATION Figure 8
The idle state for the 1 wire bus is high. If for any reason a transaction needs to be suspended, the bus
MUST be left in the idle state if the transaction is to resume. Infinite recovery time can occur between
bits so long as the 1-Wire bus is in the inactive (high) state during the recovery period. If this does not
occur and the bus is left low, all components on the bus will be reset. See Wire-1 Reset Pulse Timing
(Figure 9).
TRANSACTION SEQUENCE
The protocol for accessing the DS2438 via the 1-Wire port is as follows:
INITIALIZATION
All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence
consists of a reset pulse transmitted by the bus master followed by presence pulse(s) transmitted by the
slave(s). The presence pulse lets the bus master know that the DS2438 is on the bus and is ready to
operate. For more details, see the “1-Wire Signaling” section.
Initialization
ROM Function Command
Memory Function Command
Transaction/Data
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DS2438