Datasheet

Write Time Slots
There are two types of write time slots: write-one time
slots and write-zero time slots. The bus master uses a
write-one time slot to write a logic 1 to the device and a
write-zero time slot to write a logic 0 to the device. All write
time slots must be a minimum of 60µs in duration with a
minimum of a 1µs recovery time between individual write
slots. Both typesofwritetimeslots are initiated by the
master pulling the 1-Wire bus low (Figure10).
To generate a write-one time slot, after pulling the 1-Wire
bus low, the bus master must release the 1-Wire bus
within 15µs. When the bus is released, the 5kΩ pullup
resistor pulls the bus high. To generate a write-zero time
slot, after pulling the 1-Wire bus low, the bus master must
continue to hold the bus low for the duration of the time
slot (at least 60µs).
The device samples the 1-Wire bus during a window that
lasts from 15µs to 60µs after the master initiates the write
time slot. If the bus is high during the sampling window,
a 1 is written to the device. If the line is low, a 0 is written
to the device.
Read Time Slots
The device can only transmit data to the master when the
master issues read time slots. Therefore, the master must
generate read time slots immediately after issuing a Read
Scratchpad[BEh]orReadPowerSupply[B4h]command,
so that the device can provide the requested data. In
Figure 10. Read/Write Time Slot Timing Diagram
V
PU
1-Wire BUS
START
OF SLOT
START
OF SLOT
60µs < T
X
“0” < 120µs
1µs < t
REC
< ∞
1µs < t
REC
< ∞
> 1µs
> 1µs
MASTER SAMPLES
MASTER SAMPLES
> 1µs
15µs 15µs 30µs
MASTER WRITE-ZERO SLOT
DEVICE SAMPLES
MIN MAXTYP
DEVICE SAMPLES
MIN MAXTYP
MASTER WRITE-ONE SLOT
MASTER READ-ZERO SLOT MASTER READ-ONE SLOT
GND
V
PU
1-Wire BUS
GND
15µs 45µs 15µs
15µs 15µs 30µs
BUS MASTER PULLING LOW DEVICE PULLING LOW RESISTOR PULLUP
MAX31820 1-Wire Ambient Temperature Sensor
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