Rainbow Electronics DS28EA00 - Manual (Page 20)

DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
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SKIP ROM [CCh]
This command can save time in a single-drop bus system 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 normal Skip ROM command, the Overdrive Skip ROM sets the
DS28EA00 in the Overdrive mode (OD = 1). All communication 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 command 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 Overdrive 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 or successful Overdrive Match
command remain in Overdrive 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 or multiple devices on
the bus.