Rainbow Electronics DS1957 - Manual (Page 17)

DS1957
17 of 25
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 DS1957 on a multidrop bus and to simultaneously set it
in Overdrive Mode. Only the DS1957 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.
1-WIRE SIGNALING
The DS1957 requires strict protocols to insure data integrity. The protocol consists of five types of
signaling on one line: Reset Sequence with Reset Pulse and Presence Pulse, Write 0, Write 1, Read Data
and Strong Pull-up. All these signals except presence pulse are initiated by the bus master. The DS1957
can communicate at two different speeds, regular speed and Overdrive Speed. If not explicitly set into
the Overdrive Mode, the DS1957 will communicate at regular speed. While in Overdrive Mode the fast
timing applies to all communication-related wave forms.