DS1922E Maxim, DS1922E Datasheet - Page 34

• Manufacturer Part Number: DS1922E
• Description: The DS1922E temperature logger iButton is a rugged, self-sufficient system that measures temperature and records the result in a protected memory section
• Manufacturer: Maxim

The DS1922E requires strict protocols to ensure data
integrity. The protocol consists of four types of signaling
on one line: reset sequence with reset pulse and pres-
ence pulse, write-zero, write-one, and read-data. Except
for the presence pulse, the bus master initiates all these
signals. The DS1922E can communicate at two different
speeds: standard speed and overdrive speed. If not
explicitly set into the Overdrive Mode, the DS1922E
communicates 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
MAX
voltage to make this rise is seen in Figure 12 as “ε” and
its duration depends on the pullup resistor (R
and the capacitance of the 1-Wire network attached.
The voltage V
determining a logical level, not triggering any events.
The initialization sequence required to begin any com-
munication with the DS1922E is shown in Figure 12. A
reset pulse followed by a presence pulse indicates the
DS1922E 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
A t
Mode, returning the device to standard speed. If the
High-Temperature Logger iButton with 8KB
Data-Log Memory
Figure 12. Initialization Procedure: Reset and Presence Pulse
34
RSTL
______________________________________________________________________________________
past the threshold V
duration of 690µs or longer exits the Overdrive
V
IHMASTER
V
ILMAX
V
ILMAX
V
PUP
V
0V
TH
TL
RSTL
PUP
is relevant for the DS1922E when
+ t
below the threshold V
t
F
F
TH
to compensate for the edge.
MASTER Tx "RESET PULSE"
. The time it takes for the
1-Wire Signaling
RESISTOR
t
RSTL
PUP
TL
. To get
) used
IL-
ε
MASTER
DS1922E is in Overdrive Mode and t
than 80µs, the device remains in Overdrive Mode.
After the bus master has released the line, it goes into
receive mode (Rx). Now the 1-Wire bus is pulled to
V
DS2480B driver, through active circuitry. When the
threshold V
and then transmits a presence pulse by pulling the line
low for t
must test the logical state of the 1-Wire line at t
The t
t
t
munication. In a mixed population network, t
should be extended to minimum 480µs at standard
speed and 48µs at overdrive speed to accommodate
other 1-Wire devices.
Data communication with the DS1922E takes place in
time slots that 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
timing generator that determines when the data line is
sampled during a write time slot and how long data is
valid during a read time slot.
RSTH
PDHMAX
PUP
t
PDH
RSTH
through the pullup resistor or, in the case of a
is expired, the DS1922E is ready for data com-
t
MSP
PDL
, t
MASTER Rx "PRESENCE PULSE"
t
TH
PDLMAX
PDL
. To detect a presence pulse, the master
window must be at least the sum of
t
is crossed, the DS1922E waits for t
RSTH
, and t
TL
, the DS1922E starts its internal
t
REC
Read/Write Time Slots
RECMIN
DS1922E
. Immediately after
RSTL
is no longer
MSP
RSTH
.
PDH