DS1921L-F5X Dallas Semiconducotr, DS1921L-F5X Datasheet - Page 28

• Manufacturer Part Number: DS1921L-F5X
• Description: Thermochron iButton
• Manufacturer: Dallas Semiconducotr

INITIALIZATION PROCEDURE (RESET AND PRESENCE PULSES) Figure 13
After the bus master has released the line it goes into receive mode (RX). Now, the 1-Wire bus is pulled
to V
V
for t
The t
expired, the DS1921L is ready for data communication. In a mixed population network, t
extended to minimum 480µs at standard speed and 48µs at Overdrive speed to accommodate other 1-
Wire devices.
Read/Write Time Slots
Data communication with the DS1921L 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 14.
All communication begins with the master pulling the data line low. As the voltage on the 1-Wire line
falls below the threshold V
base creates a slave-sampling window that stretches from t
at the sampling point determines whether the DS1921L decodes the time slot as 1 or 0. For reliable
communication the voltage has to be either below the V
the entire sampling window.
Master to Slave
For a write-one time slot, the master pull-down time (t
the voltage on the 1-Wire line to reach V
latest sampling point (t
For a write-zero time slot, the master pull-down time (t
voltage on the data line below V
the next time slot can start, the voltage on the data line first needs to rise above V
until the recovery time t
TH
PDL
PUP
is crossed, the DS1921L waits for t
RSTH
. To detect a presence pulse, the master must test the logical state of the 1-Wire line at t
via the pull-up resistor or, in case of a DS2480B driver, by active circuitry. When the threshold
V
window must be at least the sum of t
IHMASTER
V
V
ILMAX
V
V
PUP
0V
TH
TL
t
F
SLSMAX
REC
RESISTOR
MASTER TX RESET PULSE
TL
is expired.
)there needs to be a recovery time (t
, the DS1921L starts its internal time base. The tolerance of the slave time
ILMAX
t
RSTL
at the sampling point of a slow DS1921L, which is t
PDH
TH
at t
and then transmits a Presence Pulse by pulling the line low
SLSMIN
PDHMAX
28 of 40
MASTER
, the earliest sampling point of a DS1921L. After the
MASTER RX PRESENCE PULSE
e
MPD1
, t
MPD0
ILMAX
PDLMAX
SLSMIN
t
PDH
= t
= t
W1L
or above the maximum V
W0L
t
MSP
, and t
REC
to t
t
PDL
-e + t
+ t
) before the next time slot can start.
SLSMAX
t
RSTH
F
RECMIN
) must be long enough to keep the
F
) must be short enough to allow
. The voltage on the data line
DS1921L
. Immediately after t
t
REC
TH
and remain there
TH
RSTH
SLSMAX
value during
MSP
should be
.
. Before
RSTH
is