Rainbow Electronics DS1821 - Manual (Page 13)

DS1821
Page 13 of 17
RELATED APPLICATION NOTES
The following Application Notes pertain to the DS1821. These notes can be obtained from the Dallas
Semiconductor “Application Note Book,” via the Dallas website at http://www.dalsemi.com or through
our faxback service at (214) 450–0441.
Application Note 67: “Applying and Using the DS1620 in Temperature Control Applications”
Application Note 74: “Reading and Writing Touch Memories via Serial Interfaces”
Application Note 105: “High Resolution Temperature Measurement with Dallas Direct-to-Digital
Temperature Sensors”
Sample 1-wire subroutines that can be used in conjunction with AN74 can be downloaded from the
Dallas website or anonymous FTP Site.
DS1821 OPERATION EXAMPLE
In this example, the master device programs the DS1821 with T
L
= +10 ° C and T
H
= +40 ° C and verifies
that the data has been saved correctly. The master then programs the status/configuration register so that
the device will power-up in thermostat mode (T/R
¯
= 1) and the thermostat output will have active high
polarity (POL = 1).
MASTER
MODE
DATA (LSB
FIRST)
COMMENTS
TX Reset Master issues reset pulse.
RX Presence DS1821 responds with presence pulse.
TX 01h Master issues Write TH command.
TX 28h Master sends data for T
H
= +40°C.
TX Reset Master issues reset pulse.
RX Presence DS1821 responds with presence pulse.
TX 02h Master issues Write TL command.
TX 0Ah Master sends data for T
L
= +10°C.
TX Reset Master issues reset pulse.
RX Presence DS1821 responds with presence pulse.
TX A1h Master issues Read TH command.
RX 28h Master reads stored T
H
value to verify data.
TX Reset Master issues reset pulse.
RX Presence DS1821 responds with presence pulse.
TX A2h Master issues Read TL command.
RX 0Ah Master reads stored T
L
value to verify data.
TX Reset Master issues reset pulse.
RX Presence DS1821 responds with presence pulse.
TX 0Ch Master issues Write Status command.
TX 06h Master sends status/configuration data to the DS1821 with T/R ¯ =
1 (thermostat mode at power-up) and POL = 1 (active high
thermostat output).
  Power is cycled; DS1821 powers-up in thermostat mode.