Skip ROM [CCh]
This command can save time in a single-drop bus sys-
tem by allowing the bus master to access the control
functions without providing the 64-bit ROM code. If
more than one slave is present on the bus and, for
example, a read command is issued following the Skip
ROM command, data collision occurs on the bus as
multiple slaves transmit simultaneously (open-drain
pulldowns produce a wired-AND result).
Overdrive-Skip ROM [3Ch]
On a single-drop bus this command can save time by
allowing the bus master to access the control functions
without providing the 64-bit ROM code. Unlike the nor-
mal Skip ROM command, the Overdrive-Skip ROM sets
the DS28EA00 in the overdrive mode (OD = 1). All com-
munication following this command has to occur at
overdrive speed until a reset pulse of minimum 480µs
duration resets all devices on the bus to standard
speed (OD = 0).
When issued on a multidrop bus, this command sets all
overdrive-supporting devices into overdrive mode. To
subsequently address a specific overdrive-supporting
device, a reset pulse at overdrive speed has to be
issued followed by a Match ROM or Search ROM com-
mand sequence. This speeds up the time for the
search process. If more than one slave supporting
overdrive is present on the bus and the Overdrive-Skip
ROM command is followed by a Read command, data
collision occurs on the bus as multiple slaves transmit
simultaneously (open-drain pulldowns produce a wired-
AND result).
Overdrive-Match ROM [69h]
The Overdrive-Match ROM command followed by a
64-bit ROM sequence transmitted at overdrive speed
allows the bus master to address a specific DS28EA00
on a multidrop bus and to simultaneously set it in over-
drive mode. Only the DS28EA00 that exactly matches
the 64-bit ROM sequence responds to the subsequent
control function command. Slaves already in overdrive
mode from a previous Overdrive-Skip ROM or success-
ful Overdrive-Match ROM command remain in over-
drive mode. All overdrive-capable slaves return to
standard speed at the next reset pulse of minimum
480µs duration. The Overdrive-Match ROM command
can be used with a single device or multiple devices on
the bus.
1-Wire Digital Thermometer with
Sequence Detect and PIO
DS28EA00
Maxim Integrated 19
