DS1923
iButton Hygrochron Temperature/Humidity
Logger with 8KB Data-Log Memory
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 code. For
example, if more than one slave is present on the bus
and 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).
Resume [A5h]
The DS1923 must be accessed several times before a
mission starts. In a multidrop environment this means
that the 64-bit ROM code after a Match ROM command
must be repeated for every access. To maximize the
data throughput in a multidrop environment, the Resume
command was implemented. This command checks the
status of the RC bit and, if it is set, directly transfers con-
trol to the memory/control functions, similar to a Skip
ROM command. The only way to set the RC bit is
through successfully executing the Match ROM, Search
ROM, or Overdrive-Match ROM command. Once the RC
bit is set, the device can repeatedly be accessed
through the Resume command. Accessing another
device on the bus clears the RC bit, preventing two or
more devices from simultaneously responding to the
Resume command.
Overdrive-Skip ROM [3Ch]
On a single-drop bus this command can save time by
allowing the bus master to access the memory/control
functions without providing the 64-bit ROM code. Unlike
the normal Skip ROM command, the Overdrive-Skip
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ROM command sets the DS1923 in the overdrive mode
(OD = 1). All communication following this command
must occur at overdrive speed until a reset pulse of
minimum 690μs 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 must 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 DS1923 on
a multidrop bus and to simultaneously set it in overdrive
mode. Only the DS1923 that exactly matches the 64-bit
ROM sequence responds to the subsequent
memory/control function command. Slaves already in
overdrive mode from a previous Overdrive-Skip ROM or
successful Overdrive-Match ROM command remain in
overdrive mode. All overdrive-capable slaves return to
standard speed at the next reset pulse of minimum
690μs duration. The Overdrive-Match ROM command
can be used with a single or multiple devices on the
bus.
Maxim Integrated