DS1921H/Z Maxim Integrated Products, DS1921H/Z Datasheet - Page 28

• Manufacturer Part Number: DS1921H/Z
• Description: High Resolution Thermochron Ibutton Range H
• Manufacturer: Maxim Integrated Products

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 DS1921H/Z is ready for data communication. In a mixed population network, t
be 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 DS1921H/Z 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 DS1921H/Z 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
the latest sampling point (t
start.
For a write-zero time slot, the master pull-down time (t
voltage on the data line below V
fore 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 DS1921H/Z 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
REC
RESISTOR
MASTER TX RESET PULSE
TL
SLSMAX
is expired.
, the DS1921H/Z starts its internal time base. The tolerance of the slave time
ILMAX
) there needs to be a recovery time (t
t
RSTL
at the sampling point of a slow DS1921H/Z, which is t
TH
PDH
at t
and then transmits a presence pulse by pulling the line low
SLSMIN
PDHMAX
28 of 40
MASTER
MASTER RX PRESENCE PULSE
, the earliest sampling point of a DS1921H/Z. After
e
MPD1
MPD0
, t
ILMAX
PDLMAX
SLSMIN
t
PDH
= t
= t
W1L
W0L
or above the maximum V
t
MSP
, and t
to t
t
-e + t
PDL
+ t
SLSMAX
t
RSTH
F
) must be long enough to keep the
RECMIN
REC
F
) must be short enough to allow
) before the next time slot can
. The voltage on the data line
DS1921H/Z
. Immediately after t
t
REC
TH
and remain there
TH
value during
RSTH
SLSMAX
MSP
.
RSTH
should
. Be-
is