Datasheet

1-Wire Signaling
The MAX31820PAR uses a strict 1-Wire communication
protocol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 8. When the device sends the
presence 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.
Figure 8. 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
MAX31820PAR 1-Wire, Parasite-Power,
Ambient Temperature Sensor
www.maximintegrated.com
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