DS1922T-F5 MAXIM [Maxim Integrated Products], DS1922T-F5 Datasheet - Page 40

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

1-Wire SIGNALING
The DS1922L/T requires strict protocols to ensure data integrity. The protocol consists of four types of signaling on
one line: reset sequence with reset pulse and presence pulse, write-zero, write-one, and read-data. Except for the
presence pulse, the bus master initiates all these signals. The DS1922L/T can communicate at two different
speeds, standard speed and Overdrive speed. If not explicitly set into the Overdrive mode, the DS1922L/T will
communicate at standard speed. While in Overdrive mode the fast timing applies to all waveforms.
To get from idle to active, the voltage on the 1-Wire line needs to fall from V
from active to idle, the voltage needs to rise from V
make this rise is seen in Figure 12 as 'ε' and its duration depends on the pullup resistor (R
capacitance of the 1-Wire network attached. The voltage V
logical level, not triggering any events.
The initialization sequence required to begin any communication with the DS1922L/T is shown in Figure 12. A reset
pulse followed by a presence pulse indicates the DS1922L/T is ready to receive data, given the correct ROM and
memory function command. If the bus master uses slew-rate control on the falling edge, it must pull down the line
for t
the device to standard speed. If the DS1922L/T is in Overdrive mode and t
will remain in Overdrive mode.
Figure 12. Initialization Procedure “Reset and Presence Pulses”
After the bus master has released the line it goes into receive mode (RX). Now the 1-Wire bus is pulled to V
through the pullup resistor or, in case of a DS2480B driver, by active circuitry. When the threshold V
the DS1922L/T waits for t
presence pulse, the master must test the logical state of the 1-Wire line at t
The t
DS1922L/T is ready for data communication. In a mixed population network t
480µs at standard speed and 48µs at Overdrive speed to accommodate other 1-Wire devices.
READ/WRITE TIME SLOTS
Data communication with the DS1922L/T takes place in time slots, which carry a single bit each. Write time slots
transport data from bus master to slave. Read time slots transfer data from slave to master. The definitions of the
write and read time slots are illustrated in Figure 13.
All communication begins with the master pulling the data line low. As the voltage on the 1-Wire line falls below the
threshold V
during a write time slot and how long data is valid during a read time slot.
RSTL
RSTH
+ t
window must be at least the sum of t
F
V
TL
to compensate for the edge. A t
IHMASTER
, the DS1922L/T starts its internal timing generator that determines when the data line is sampled
V
V
ILMAX
V
V
PUP
0V
TH
TL
t
F
RESISTOR
MASTER TX “RESET PULSE” MASTER RX “PRESENCE PULSE”
PDH
and then transmits a presence pulse by pulling the line low for t
t
RSTL
RSTL
PDHMAX
duration of 690µs or longer will exit the Overdrive mode returning
ILMAX
40 of 50
, t
past the threshold V
MASTER
PDLMAX
ILMAX
ε
, and t
is relevant for the DS1922L/T when determining a
t
PDH
RECMIN
t
MSP
t
PDL
MSP
. Immediately after t
t
RSTH
RSTL
TH
.
RSTH
PUP
. The time it takes for the voltage to
is no longer than 80µs the device
should be extended to minimum
below the threshold V
DS1922L/T
t
REC
DS1922L/DS1922T
RSTH
PUP
PDL
) used and the
is expired, the
TH
. To detect a
is crossed,
TL
. To get
PUP