Datasheet

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] command, so that the device
can provide the requested data. In addition, the master
can generate read time slots after issuing a Recall E
2
[B8h]commandtofindoutthestatusoftheoperation,as
explained in the Parasite Power section.
All read time slots must be a minimum of 60µs in duration
with a minimum of a 1µs recovery time between slots. A
read time slot is initiated by the master device pulling the
1-Wire bus low for a minimum of 1µs and then releasing
the bus (
Figure9). After the master initiates the read time
slot, the device begins transmitting a 1 or 0 on the bus.
The device transmits a 1 by leaving the bus high and
transmits a 0 by pulling the bus low. When transmitting
a 0, the device releases the bus by the end of the time
slot, and the bus is pulled back to its high idle state by
the pullup resister. Output data from the device is valid
for 15µs after the falling edge that initiated the read time
slot. Therefore, the master must release the bus and then
sample the bus state within 15µs from the start of the slot.
Figure 10 illustrates that the sum of t
INIT
, t
RC
, and
t
SAMPLE
must be less than 15µs for a read time slot.
Figure11 shows that system timing margin is maximized
by keeping t
INIT
and t
RC
as short as possible and by
locating the master sample time during read time slots
towards the end of the 15µs period.
Figure 10. Detailed Master Read-One Timing
Figure 11. Recommended Master Read-One Timing
V
IH
OF MASTER
MASTER SAMPLES
V
PU
1-Wire BUS
GND
15µs
t
INIT
> 1µs t
RC
BUS MASTER PULLING LOW RESISTOR PULLUP
V
PU
V
IH
OF MASTER
t
INIT
=
SMALL
t
RC
=
SMALL
MASTER SAMPLES
15µs
1-Wire BUS
GND
BUS MASTER PULLING LOW RESISTOR PULLUP
MAX31820PAR 1-Wire, Parasite-Power,
Ambient Temperature Sensor
www.maximintegrated.com
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