DS1921Z-F5# Maxim Integrated Products, DS1921Z-F5# Datasheet - Page 31

• Manufacturer Part Number: DS1921Z-F5#
• Description: IBUTTON THERMOCHRON F5
• Manufacturer: Maxim Integrated Products
• Series: iButton®r

Specifications of DS1921Z-F5#

• Rohs Information: IButton RoHS Compliance Plan
• Memory Size: 512B
• Memory Type: NVSRAM (Non-Volatile SRAM)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

On a single-drop bus this command can save time by
allowing the bus master to access the memory/control
functions without providing the 64-bit ROM code. Unlike
the normal Skip ROM command, the Overdrive-Skip
ROM command sets the DS1921G in the overdrive
mode (OD = 1). All communication following this com-
mand must occur at overdrive speed until a reset pulse
of minimum 480µs duration resets all devices on the
bus to standard speed (OD = 0).
When issued on a multidrop bus, this command sets all
overdrive-supporting devices into overdrive mode. To
subsequently address a specific overdrive-supporting
device, a reset pulse at overdrive speed must be
issued followed by a Match ROM or Search ROM com-
mand sequence. This speeds up the time for the
search process. If more than one slave supporting
overdrive is present on the bus and the Overdrive-Skip
ROM command is followed by a read command, data
collision occurs on the bus as multiple slaves transmit
simultaneously (open-drain pulldowns produce a wired-
AND result).
The Overdrive-Match ROM command followed by a 64-
bit ROM sequence transmitted at overdrive speed
allows the bus master to address a specific DS1921G
on a multidrop bus and to simultaneously set it in over-
drive mode. Only the DS1921G that exactly matches
the 64-bit ROM sequence responds to the subsequent
memory/control function command. Slaves already in
overdrive mode from a previous Overdrive-Skip or suc-
cessful Overdrive-Match ROM command remain in
overdrive mode. All overdrive-capable slaves return to
Figure 14. Intitialization Procedure: Reset and Presence Pulses
V
IHMASTER
V
ILMAX
V
V
PUP
V
0V
TH
TL
______________________________________________________________________________________
Overdrive-Match ROM [69h]
Overdrive-Skip ROM [3Ch]
t
F
MASTER Tx "RESET PULSE"
RESISTOR
t
RSTL
ε
MASTER
standard speed at the next reset pulse of minimum
480µs duration. The Overdrive-Match ROM command
can be used with a single or multiple devices on the
bus.
The DS1921G 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 DS1921G can communicate at two different
speeds: standard speed and overdrive speed. If not
explicitly set into the overdrive mode, the DS1921G
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
voltage to make this rise is seen in Figure 14 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, but not for triggering any
events.
The initialization sequence required to begin any com-
munication with the DS1921G is shown in Figure 14. A
reset pulse followed by a presence pulse indicates the
DS1921G 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
ILMAX
t
PDH
Thermochron iButton
t
MSP
past the threshold V
MASTER Rx "PRESENCE PULSE"
t
PDL
ILMAX
t
RSTH
RSTL
PUP
is relevant for the DS1921G when
+ t
below the threshold V
F
t
REC
to compensate for the edge.
TH
DS1921G
1-Wire Signaling
. The time it takes for the
PUP
TL
. To get
) used
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