DS1825U+T&R【PDF 17/21 页】IC THERMOMETER DIGITAL 8-USOP

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DS1825 Programmable Resolution 1-Wire Digital Thermometer With 4-Bit ID

17 of 21

Figure 15. READ/WRITE TIME SLOT TIMING DIAGRAM

READ TIME SLOTS

The DS1825 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 DS1825 can provide the requested data. In addition, the master can generate read time slots

after issuing Convert T [44h] or Recall E

[B8h] commands to find out the status of the operation as explained in

the DS1825 FUNCTION COMMAND section.

All read time slots must be a minimum of 60ms in duration with a minimum of a 1ms recovery time between slots. A

read time slot is initiated by the master device pulling the 1-Wire bus low for a minimum of 1ms and then releasing

the bus (see Figure 14). After the master initiates the read time slot, the DS1825 will begin transmitting a 1 or 0 on

bus. The DS1825 transmits a 1 by leaving the bus high and transmits a 0 by pulling the bus low. When transmitting

a 0, the DS1825 will release the bus by the end of the time slot, and the bus will be pulled back to its high idle state

by the pullup resister. Output data from the DS1825 is valid for 15ms after the falling edge that initiated the read

time slot. Therefore, the master must release the bus and then sample the bus state within 15ms from the start of

the slot.

Figure 15 illustrates that the sum of T

INIT

, T

, and T

SAMPLE

must be less than 15ms for a read time slot. Figure 16

shows that system timing margin is maximized by keeping T

INIT

and T

as short as possible and by locating the

master sample time during read time slots towards the end of the 15ms period.

45 ms

15 ms

GND

1-WIRE BUS

60 ms < T

0 < 120 ms

1 ms < T

REC

< ?/SPAN>

DS1825 Samples

MIN TYP MAX

15 ms

30 ms

> 1 ms

MASTER WRITE 0 SLOT

MASTER WRITE 1 SLOT

GND

1-WIRE BUS

15 ms

MASTER READ 0 SLOT

MASTER READ 1 SLOT

Master samples

START

OF SLOT

START

OF SLOT

> 1 ms

1 ms < T

REC

< ?/SPAN>

15 ms

30 ms

15 ms

DS1825 Samples

MIN TYP MA

LINE TYPE LEGEND

Bus master pulling low

DS1825 pulling low

Resistor pullup

> 1 ms

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