Datasheet

DS28E05 1-Wire EEPROM
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A multidrop bus consists of a 1-Wire bus with multiple
slaves attached. The DS28E05 supports overdrive speed
of76.9kbps(max)onlyandcannotbeusedtogetherwith
standard speed or dual-speed 1-Wire slaves on the bus.
The value of the pullup resistor primarily depends on the
1-Wirepullupvoltage,networksizeandloadconditions.
The DS28E05 requires a pullup resistor of maximum
1.5kΩ.
The idle state for the 1-Wire bus is high. If for any reason
atransactionmustbesuspended,thebusmustbeleftin
the idle state if the transaction is to resume. If this does
notoccurandthebusisleftlowformorethan16µs,one
or more devices on the bus could be reset.
Transaction Sequence
The protocol for accessing the DS28E05 through the
1-Wireportisasfollows:
• Initialization
• ROMFunctionCommand
• MemoryFunctionCommand
• Transaction Data
Initialization
Alltransactionsonthe1-Wirebusbeginwithaninitializa-
tion 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 pres-
ence pulse lets the bus master know that the DS28E05 is
onthebusandisreadytooperate.Formoredetails,see
the 1-Wire Signaling section.
1-Wire ROM Function Commands
Once the bus master has detected a presence, it can
issue one of the five ROM function commands that the
DS28E05 supports.All ROM function commands are 8
bitslong.Alistofthesecommandsfollows(seetheflow-
chart in
Figure8).
Read ROM [33h]
The Read ROM command allows the bus master to read
theDS28E05’sROMID(8-bitfamilycode,unique48-bit
serialnumber,and8-bitCRC).Thiscommand can only
be used if there is a single slave on the bus. If more than
oneslaveispresentonthebus,adatacollisionoccurs
when all slaves try to transmit at the same time (open
drainproducesawired-ANDresult).Thefamilycodeand
48-bit serial number as read by the master are unlikely to
matchtheCRC.
Match ROM [55h]
TheMatchROMcommand,followedbya64-bitROMID,
allows the bus master to address a specific DS28E05 on
a multidrop bus. Only the DS28E05 that exactly matches
the 64-bit ROM ID responds to the following memory
functioncommand.Allotherslaveswaitforaresetpulse.
This command can be used with a single or multiple
devices on the bus.
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 ROM ID numbers. By taking advantage of the
wired-ANDpropertyofthebus,themastercanuseapro-
cess of elimination to identify the ID of all slave devices.
ForeachbitoftheIDnumber,startingwiththeleastsig-
nificantbit,thebusmasterissuesatripletoftimeslots.
On the first slot, each slave device participating in the
search outputs the true value of its ID number bit. On the
secondslot,eachslavedeviceparticipatinginthesearch
outputs the complemented value of its ID number bit. On
thethirdslot,themasterwritesthetruevalueofthebit
to be selected.All slave devices that do not match the
bit written by the master stop participating in the search.
Ifbothofthe readbitsarezero,themasterknows that
slavedevicesexistwithbothstatesofthebit.Bychoos-
ingwhichstatetowrite,thebusmasterbranchesinthe
search tree. After one complete pass, the bus master
knowstheROMIDnumberofasingledevice.Additional
passes identify the ID numbers of the remaining devices.
Refer to
ApplicationNote187:1-Wire Search Algorithm
foradetaileddiscussion,includinganexample.
Skip ROM [CCh]
This command can save time in a single-drop bus sys-
tem by allowing the bus master to access the memory
functions without providing the 64-bit ROM ID. If more
thanoneslaveispresent on thebusand,forexample,
a read command is issued following the Skip ROM com-
mand,datacollisionoccursonthebusasmultipleslaves
transmit simultaneously (open-drain pulldowns produce a
wired-ANDresult).