DS2450

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102199

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

µs 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

µs duration. The Overdrive Match ROM

command can be used with a single or multiple devices on the bus.