DS1992/DS1993

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Figure 10. INITIALIZATION PROCEDURE RESET AND PRESENCE PULSE

RESISTOR

MASTER

DS199x

MASTER RX "PRESENCE PULSE"

480 µs ≤ t

480 µs ≤ t

15 µs ≤ t

60 ≤ t

MASTER TX

"RESET PULSE"

V

PULLUP

V

PULLUP MIN

V

IL MAX

0V

t

PDH

t

R

* In order not to mask interrup signaling

** Includes recovery time

READ/WRITE TIME SLOTS

The definitions of write and read time slots are illustrated in Figure 11. The master driving the data line

low initiates all time slots. The falling edge of the data line synchronizes the DS199x to the master by

triggering a delay circuit in the DS199x. During write time slots, the delay circuit determines when the

DS199x samples the data line. For a read data time slot, if a 0 is to be transmitted, the delay circuit

determines how long the DS199x holds the data line low overriding the 1 generated by the master. If the

data bit is a 1, the iButton leaves the read data time slot unchanged.

Figure 11. READ/WRITE TIMING DIAGRAM

Write-One Time Slot

15µs

60µs

DS199x

Sampling Window

V

PULLUP MIN

0V

t

SLOT

t

REC

t

LOW1

60 µs ≤ t

1 µs ≤ t

1 µs ≤ t

RESISTOR

MASTER