Rainbow Electronics DS2422 - Manual (Page 16)

DS2422/DS2423
16 of 25
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 DS242X on a multidrop bus and to simultaneously set it
in Overdrive mode. Only the DS242X 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 other slaves that do not match the 64-bit
ROM sequence or do not support Overdrive will return to or remain at regular speed and wait for a Reset
Pulse of minimum 480 µs duration. The Overdrive Match ROM command can be used with a single or
multiple devices on the bus.