DS1922T-F5 MAXIM [Maxim Integrated Products], DS1922T-F5 Datasheet - Page 37

• Manufacturer Part Number: DS1922T-F5
• Description: Temperature Logger iButton With 8kB Datalog Memory
• Manufacturer: MAXIM [Maxim Integrated Products]

DS1922L/DS1922T
RESUME COMMAND [A5h]
The DS1922L/T needs to be accessed several times before a mission will start. In a multidrop environment this
means that the 64-bit ROM code after a Match ROM command has to be repeated for every access. To maximize
the data throughput in a multidrop environment, the Resume function was implemented. This function checks the
status of the RC bit and, if it is set, directly transfers control to the Memory/Control functions, similar to a Skip ROM
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 clears 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 DS1922L/T 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 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 DS1922L/T on a multidrop bus and to simultaneously set it in Overdrive mode.
Only the DS1922L/T that exactly matches the 64-bit ROM sequence responds to the subsequent memory/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 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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