DS1921H_11 MAXIM [Maxim Integrated Products], DS1921H_11 Datasheet - Page 30

• Manufacturer Part Number: DS1921H_11
• Description: High-Resolution Thermochron iButton
• Manufacturer: MAXIM [Maxim Integrated Products]

DS1921H/Z
INITIALIZATION PROCEDURE (RESET AND PRESENCE PULSES) Figure 14
After the bus master has released the line it goes into receive mode (RX). Now, the 1-Wire bus is pulled
to V
via the pull-up resistor or, in case of a DS2480B driver, by active circuitry. When the threshold
PUP
V
is crossed, the DS1921H/Z waits for t
and then transmits a presence pulse by pulling the line low
TH
PDH
for t
. To detect a presence pulse, the master must test the logical state of the 1-Wire line at t
.
PDL
MSP
The t
window must be at least the sum of t
, t
, and t
. Immediately after t
is
RSTH
PDHMAX
PDLMAX
RECMIN
RSTH
expired, the DS1921H/Z is ready for data communication. In a mixed population network, t
should
RSTH
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 15.
All communication begins with the master pulling the data line low. As the voltage on the 1-Wire line
falls below the threshold V
, the DS1921H/Z starts its internal timing generator that determines when
TL
the data line will be sampled during a write time slot and how long data will be valid during a read time
slot.
Master to Slave
For a write-one time slot, the voltage on the data line must have crossed the V
threshold after the
TH
write-one low time t
is expired. For a write-zero time slot, the voltage on the data line must stay
W1LMAX
below the V
threshold until the write-zero low time t
is expired. The voltage on the data line
TH
W0LMIN
should not exceed V
during the entire t
or t
window. After the V
threshold has been
ILMAX
W0L
W1L
TH
crossed, the DS1921H/Z needs a recovery time t
before it is ready for the next time slot.
REC
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