DS1921 DALLAS [Dallas Semiconductor], DS1921 Datasheet - Page 30

• Manufacturer Part Number: DS1921
• Description: High-Resolution Thermochron iButton
• Manufacturer: DALLAS [Dallas Semiconductor]

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
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 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 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
write-one low time t
below the V
should not exceed V
crossed, the DS1921H/Z needs a 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
TH
V
V
ILMAX
V
V
PUP
0V
threshold until the write-zero low time t
TH
TL
t
W1LMAX
F
ILMAX
RESISTOR
MASTER TX RESET PULSE
TL
during the entire t
is expired. For a write-zero time slot, the voltage on the data line must stay
, the DS1921H/Z starts its internal timing generator that determines when
t
RSTL
PDH
and then transmits a presence pulse by pulling the line low
W0L
REC
PDHMAX
30 of 44
MASTER
before it is ready for the next time slot.
or t
MASTER RX PRESENCE PULSE
, t
W1L
W0LMIN
PDLMAX
t
PDH
window. After the V
t
MSP
, and t
is expired. The voltage on the data line
t
PDL
t
RSTH
RECMIN
DS1921H/Z
. Immediately after t
t
REC
TH
TH
threshold has been
threshold after the
RSTH
MSP
DS1921H/Z
.
RSTH
should
is