Datasheet

Recall E
2
[B8h]
This command recalls the alarm trigger values (T
H
and
T
L
)andconfigurationdatafromEEPROMandplacesthe
data in bytes 2, 3, and 4, respectively, in the scratchpad
memory. The master device can issue read time slots fol-
lowing the Recall E
2
command and the device indicates
the status of the recall by transmitting 0 while the recall
is in progress and 1 when the recall is done. The recall
operation happens automatically at power-up, so valid
data is available in the scratchpad as soon as power is
applied to the device.
Read Power Supply [B4h]
The master device issues this command followed by a
read time slot to determine if any devices on the bus are
usingparasitepower.Duringthereadtimeslot,parasite-
powered devices pull the bus low, and externally pow-
ereddevicesletthebusremainhigh.SeethePowering
the MAX31820 section for usage information for this
command.
1-Wire Signaling
The MAX31820 uses a strict 1-Wire communication pro-
tocol to ensure data integrity. Several signal types are
definedbythisprotocol:resetpulse,presencepulse,write
0, write 1, read 0, and read 1. The bus master initiates all
these signals, with the exception of the presence pulse.
Initialization Procedure: Reset and Presence
Pulses
All communication with the device begins with an initial-
ization sequence that consists of a reset pulse from the
master followed by a presence pulse from the device, as
illustrated in
Figure9. When the device sends the pres-
ence pulse in response to the reset, it is indicating to the
master that it is on the bus and ready to operate.
During the initialization sequence, the bus master
transmits (T
X
) the reset pulse by pulling the 1-Wire bus
low for a minimum of 480µs. The bus master then releas-
es the bus and goes into receive mode (R
X
). When the
busisreleased,the5kΩpullupresistorpullsthe1-Wire
bus high. When the device detects this rising edge, it
waits 15µs to 60µs and then transmits a presence pulse
by pulling the 1-Wire bus low for 60µs to 240µs.
Read/Write Time Slots
The bus master writes data to the device during write time
slots and reads data from the device during read time
slots. One bit of data is transmitted over the 1-Wire bus
per time slot.
Figure 9. Initialization Timing
V
PU
1-Wire BUS
MASTER T
X
RESET PULSE
480µs MINIMUM
MASTER R
X
480µs MINIMUM
DEVICE T
X
PRESENCE PULSE
60µs TO 240µs
DEVICE WAITS
15µs TO 60µs
GND
BUS MASTER PULLING LOW DEVICE PULLING LOW RESISTOR PULLUP
MAX31820 1-Wire Ambient Temperature Sensor
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