DS1920

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READ/WRITE TIME SLOTS

The definitions of write and read time slots are illustrated in Figure 11. All time slots are initiated by the

master driving the data line low. The falling edge of the data line synchronizes the DS1920 to the master

by triggering a delay circuit in the DS1920. During write time slots, the delay circuit determines when the

DS1920 will sample the data line. For a read data time slot, if a 0 is to be transmitted, the delay circuit

determines how long the DS1920 will hold the data line low overriding the 1 generated by the master. If

the data bit is a 1, the DS1920 will leave the read data time slot unchanged.

STRONG PULLUP

To provide energy for a temperature conversion or for copying data from the scratchpad to the EEPROM,

a low impedance pullup of the 1-Wire bus to 5V is required just after the corresponding command has

been sent by the master. During temperature conversion or copying the scratchpad, the bus master

controls the transition from a state where the data line is idling high via the pullup resistor to a state where

the data line is actively driven to 5 volts, providing a minimum of 1 mA of current for each DS1920

doing temperature conversion. This low impedance pullup should be active for 0.5 seconds for

temperature conversion or at least 10 ms for copying to the scratchpad. After that, the data line returns to

an idle high state controlled by the pullup resistor. The low-impedance pullup does not affect other

devices on the 1-Wire bus. Therefore it is possible to multidrop other 1-Wire devices with the DS1920.

INITIALIZATION PROCEDURE “RESET AND PRESENCE PULSES” Figure 10

480

µs ≤t

∞ ∗

480

µs ≤t

∞ (includes recovery time)

15

µs ≤t

µs

60

µs ≤t

µs

*

be less than 960

µs.

RESISTOR

MASTER

DS1920