DS2438Z Maxim Integrated Products, DS2438Z Datasheet - Page 18

• Manufacturer Part Number: DS2438Z
• Description: IC MONITOR SMART BATTERY 8-SOIC
• Manufacturer: Maxim Integrated Products

Specifications of DS2438Z

• Function: Fuel, Gas Gauge/Monitor
• Battery Type: Smart Batteries
• Voltage - Supply: 2.4 V ~ 10 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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 8-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 DS2438’s 8-bit family code (26h), unique 48-bit serial
number, and 8-bit CRC. This command can only be used if there is a single DS2438 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 DS2438 on a multidrop bus. Only the DS2438 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 pull-downs will produce a wired-AND result).
Search ROM [F0h]
When a system is initially brought up, the bus master might not know the number of devices on the 1-
Wire bus or their 64-bit ROM codes. The search ROM command allows the bus master to use a process
of elimination to identify the 64-bit ROM codes of all slave devices on the bus.
Example of a ROM Search
The ROM search process is the repetition of a simple three-step routine: read a bit, read the complement
of the bit, then write the desired value of that bit. The bus master performs this simple, three-step routine
on each bit of the ROM. After one complete pass, the bus master knows the contents of the ROM in one
device. The remaining number of devices and their ROM codes may be identified by additional passes.
The following example of the ROM search process assumes four different devices are connected to the
same 1-Wire bus. The ROM data of the four devices is as shown (LSb first):
The search process is as follows:
1. The bus master begins the initialization sequence by issuing a reset pulse. The slave devices respond
2. The bus master will then issue the search ROM command on the 1-Wire bus (F0h).
by issuing simultaneous presence pulses.
ROM1 = 00110101...
ROM2 = 10101010...
ROM3 = 11110101...
ROM4 = 00010001...
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