DS1820
021497 16/27
INITIALIZATION PROCEDURE “RESET AND PRESENCE PULSES” Figure 11
Master T
X
“reset pulse”
480
µ
s minimum
960
µ
s maximum
Master R
X
480
µ
s minimum
V
CC
GND
DS1820
waits
15 - 60
µ
s
DS1820 T
X
“presence pulse”
60 - 240
µ
s
LINE TYPE LEGEND:
Bus master active low
Both bus master and
DS1820 active low
DS1820 active low
Resistor pull–up
1–WIRE
BUS
DS1820 COMMAND SET Table 2
INSTRUCTION
DESCRIPTION
PROTOCOL
1–WIRE BUS
AFTER ISSUING
PROTOCOL
NOTES
TEMPERATURE CONVERSION COMMANDS
Convert T
Initiates temperature conversion.
44h
<read temperature
busy status>
1
MEMORY COMMANDS
Read Scratchpad
Reads bytes from scratchpad and
reads CRC byte.
BEh
<read data up to 9
bytes>
Write Scratchpad
Writes bytes into scratchpad at
addresses 2 and 3 (TH and TL
temperature triggers).
4Eh
<write data into 2
bytes at addr. 2 and
addr. 3>
Copy Scratchpad
Copies scratchpad into nonvolatile
memory (addresses 2 and 3 only).
48h
<read copy status>
2
Recall E
2
Recalls values stored in nonvolatile
memory into scratchpad (tempera-
ture triggers).
B8h
<read temperature
busy status>
Read Power Supply
Signals the mode of DS1820
power supply to the master.
B4h
<read supply status>
NOTES:
1. Temperature conversion takes up to 500 ms. After receiving the Convert T protocol, if the part does not
receive power from the V
DD
pin, the I/O line for the DS1820 must be held high for at least 500 ms to provide
power during the conversion process. As such, no other activity may take place on the 1–Wire bus for at least
this period after a Convert T command has been issued.
2. After receiving the Copy Scratchpad protocol, if the part does not receive power from the V
DD
pin, the I/O line
for the DS1820 must be held high for at least 10 ms to provide power during the copy process. As such, no
other activity may take place on the 1–Wire bus for at least this period after a Copy Scratchpad command has
been issued.
