DS2422 Maxim, DS2422 Datasheet - Page 37

• Manufacturer Part Number: DS2422
• Description: The DS2422 temperature/data logger combines the core functions of a fully featured data logger in a single chip
• Manufacturer: Maxim

DS2422
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 function. Accessing another device on the bus will clear the RC bit, preventing two or more
devices from simultaneously responding to the Resume Command function.
OVERDRIVE SKIP ROM [3Ch]
On a single-drop bus this command can save time by allowing the bus master to access the memory/control func-
tions without providing the 64-bit ROM code. Unlike the normal Skip ROM command, the Overdrive Skip ROM sets
the DS2422 in the Overdrive mode (OD = 1). All communication following this command has to 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 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 DS2422 on a multidrop bus and to simultaneously set it in Overdrive mode.
Only the DS2422 that exactly matches the 64-bit ROM sequence will respond to the subsequent memory/control
function command. Slaves already in Overdrive mode from a previous Overdrive Skip or successful Overdrive
Match command will remain in Overdrive mode. All overdrive-capable slaves will 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.
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