ds2437 Maxim Integrated Products, Inc., ds2437 Datasheet - Page 17

• Manufacturer Part Number: ds2437
• Description: Smart Battery Monitor
• Manufacturer: Maxim Integrated Products, Inc.

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 for more than 480 s, all components on the bus will be reset.
TRANSACTION SEQUENCE
The protocol for accessing the DS2437 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 DS2437 is on the bus and is ready to operate. For
more details, see the “1-Wire Signaling” section.
ROM FUNCTION COMMANDS
Once the bus master has detected a presence, it can issue one of the four ROM function commands. All
ROM function commands are eight bits long. A list of these commands follows (refer to flowchart in
Figure 5):
Read ROM [33h]
This command allows the bus master to read the DS2437’s 8-bit family code (1Eh), unique 48-bit serial
number, and 8-bit CRC. This command can only be used if there is a single DS2437 on the bus. If more
than one slave is present on the bus, a data collision will occur when all slaves try to transmit at the same
time (open-drain will produce a wired-AND result).
Match ROM [55h]
The Match ROM command, followed by a 64-bit ROM sequence, allows the bus master to address a
specific DS2437 on a multidrop bus. Only the DS2437 that exactly matches the 64-bit ROM sequence
will respond to the following memory function command. All slaves that do not match the 64-bit ROM
sequence will wait for a reset pulse. This command can be used with a single or multiple devices on the
bus.
Skip ROM [CCh]
This command can save time in a single-drop bus system by allowing the bus master to access the
memory functions without providing the 64-bit ROM code. If more than one slave is present on the bus
and a read command is issued following the Skip ROM command, data collision will occur on the bus as
multiple slaves transmit simultaneously (open drain pulldowns will produce a wired-AND result).
Initialization
ROM Function Command
Memory Function Command
Transaction/Data
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DS2437