DS2450
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CONDITIONAL SEARCH [ECH]
The Conditional Search ROM command operates similarly to the Search ROM command except that only
devices fulfilling the specified condition will participate in the search. The DS2450 will respond to the
Conditional Search command if a channel’s alarm enable flags AEH and/or AEL are set and the
conversion results in a value outside the range specified by the channel’s alarm threshold voltages. See
section Device Registers for details. The Conditional Search ROM provides an efficient means for the
bus master to determine devices on a multidrop system that have to signal an important event, such as a
voltage leaving the tolerance band. After each pass of the Conditional Search that successfully
determined the 64-bit ROM for a specific device on the multidrop bus, that particular device can be
individually accessed as if a Match ROM had been issued since all other devices will have dropped out of
the search process and are waiting for a reset pulse.
OVERDRIVE SKIP ROM [3CH]
On a single-drop bus this command can save time by allowing the bus master to access the
memory/convert functions without providing the 64-bit ROM code. Unlike the normal Skip ROM
command the Overdrive Skip ROM sets the DS2450 in the Overdrive Mode (OD = 1). All
communication following this command has to occur at Overdrive Speed until a reset pulse of minimum
480
μ
s duration resets all devices on the bus to regular speed (OD = 0).
When issued on a multidrop bus this command will set 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 command sequence. This will speed 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 will occur on the bus as
multiple slaves transmit simultaneously (open drain pulldowns will 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 DS2450 on a multidrop bus and to simultaneously set it
in Overdrive Mode. Only the DS2450 that exactly matches the 64-bit ROM sequence will respond to the
subsequent memory function command. Slaves already in Overdrive mode from a previous Overdrive
Skip or Match command will remain in Overdrive mode. All overdrive-capable slaves will return to
regular speed at the next Reset Pulse of minimum 480
μ
s duration. The Overdrive Match ROM
command can be used with a single or multiple devices on the bus.