1DS1821(3)                    One-Wire File System                    DS1821(3)
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NAME

6       DS1821 - Programmable Digital Thermostat and Thermometer
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SYNOPSIS

9       Thermostat.
10
11       thermostat  [/[  temperature | temphigh | templow | temphighflag | tem‐
12       plowflag | thermostatmode | polarity | 1shot ]]
13

FAMILY CODE

15       none
16

SPECIAL PROPERTIES

18   temperature
19       read-only, floating point
20       9-bit resolution temperature. Units are selected from the invoking com‐
21       mand  line.  See owfs(1) or owhttpd(1) for choices. Default is Celsius.
22       Conversion takes 1 second.
23
24   temphigh templow
25       read-write. floating point
26       Temperature limits for alarms. Units are  selected  from  the  invoking
27       command  line.  See  owfs(1) or owhttpd(1) for choices. Default is Cel‐
28       sius.
29       Note that alarms are not implemented.
30
31   temphighflag, templowflag
32       read-write. yes-no
33       temphighflag goes to 1 when temperature exceeds temphigh and stays at 1
34       until  it  is  reset by writing it to zero.  This state persists across
35       power cycles and operates in both 1-wire and  thermostat  modes.   tem‐
36       plowflag  behaves  in  the  same  way,  monitoring the temperature with
37       respect to templow.
38
39   thermostatmode
40       read-write. yes-no
41       When this bit is set to 1 the chip will enter thermostat  mode  on  the
42       next power-up.  See the datasheet for further information on thermostat
43       mode.  NOTE: Once the DS1821 has entered thermostat mode it  cannot  be
44       taken  out back to 1-wire mode using a 1-wire interface.  Special elec‐
45       trical incantations on the power and data lines must be performed  that
46       are  not possible with a normal 1-wire bus master. A special circuit is
47       required - see the datasheet for complete details.
48
49   polarity
50       read-write. yes-no
51       Controls the output sense of the thermostat output (DQ) while in  ther‐
52       mostat  mode.   If  polarity is 0 the output is active low. If it is 1,
53       active high.
54
55   1shot
56       read-write. yes-no
57       If this bit is 1, a START CONVERT command will begin a  conversion  and
58       the  chip will enter a low power state when the conversion is complete.
59       If the bit is 0 then START CONVERT will begin a  conversion  and  start
60       another  one  as soon as it is done.  STOP CONVERSION must be performed
61       to get the conversion cycle  to  stop.   This  interface  automatically
62       issues a STOP CONVERSION command when going out of continuous mode.
63

TEMPERATURE ALARM LIMITS

65       When  the device exceeds either temphigh or templow temperature thresh‐
66       old the device is in the alarm state, and  will  appear  in  the  alarm
67       directory.  This provides an easy way to poll for temperatures that are
68       unsafe, especially if simultaneous temperature conversion is done.
69
70       Units for the temperature alarms are in the same temperature scale that
71       was set for temperature measurements.
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73       Temperature  thresholds  are  stored in non-volatile memory and persist
74       until changed, even if power is lost.
75
76   temphigh
77       read-write, integer
78       Shows or sets the lower limit for the high temperature alarm state.
79
80   templow
81       read-write, integer
82       Shows or sets the upper limit for the low temperature alarm state.
83

STANDARD PROPERTIES

85   type
86       read-only, ascii
87       Chip type: DS1821
88

DESCRIPTION

90   1-Wire
91       1-wire is a wiring protocol and series of devices designed and manufac‐
92       tured  by  Dallas  Semiconductor, Inc. The bus is a low-power low-speed
93       low-connector scheme where the data line can also provide power.
94
95       Each device is uniquely and unalterably  numbered  during  manufacture.
96       There  are a wide variety of devices, including memory, sensors (humid‐
97       ity, temperature, voltage, contact, current), switches, timers and data
98       loggers.  More complex devices (like thermocouple sensors) can be built
99       with these basic devices. There  are  also  1-wire  devices  that  have
100       encryption included.
101
102       The  1-wire  scheme uses a single bus master and multiple slaves on the
103       same wire. The bus master initiates all communication. The  slaves  can
104       be individually discovered and addressed using their unique ID.
105
106       Bus  masters come in a variety of configurations including serial, par‐
107       allel, i2c, network or USB adapters.
108
109   OWFS design
110       OWFS is a suite of programs that designed to make the  1-wire  bus  and
111       its  devices easily accessible. The underlying principle is to create a
112       virtual filesystem, with the unique ID being  the  directory,  and  the
113       individual  properties  of  the  device are represented as simple files
114       that can be read and written.
115
116       Details of the individual slave or master design are  hidden  behind  a
117       consistent interface. The goal is to provide an easy set of tools for a
118       software designer to create monitoring or control  applications.  There
119       are some performance enhancements in the implementation, including data
120       caching, parallel access to bus masters, and aggregation of device com‐
121       munication.  Still the fundamental goal has been ease of use, flexibil‐
122       ity and correctness rather than speed.
123
124   DS1821
125       The DS1821 (3) is a unique 1-wire  device.  It  is  unaddressable,  and
126       therefore there can be only one on a given bus.  It is meant to be pro‐
127       grammed once using 1-wire and then permanently installed in  a  thermo‐
128       stat  circuit.   Once  in thermostat mode, it is no longer programmable
129       from a 1-wire interface.  It is possible to recover it into 1-wire mode
130       but only with a special circuit.
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132

ADDRESSING

134       Unlike all other 1-wire chips, the ,B DS1821 (3) has no unique address.
135       It is addressed as thermostat and will not announce  itself  in  device
136       discovery (directory listing).
137

DATASHEET

139       http://pdfserv.maxim-ic.com/en/ds/DS1821.pdf
140

SEE ALSO

142   Programs
143       owfs  (1)  owhttpd  (1)  owftpd  (1)  owserver (1) owdir (1) owread (1)
144       owwrite (1) owpresent (1) owtap (1)
145
146   Configuration and testing
147       owfs (5) owtap (1) owmon (1)
148
149   Language bindings
150       owtcl (3) owperl (3) owcapi (3)
151
152   Clocks
153       DS1427 (3) DS1904 (3) DS1994 (3) DS2404  (3)  DS2404S  (3)  DS2415  (3)
154       DS2417 (3)
155
156   ID
157       DS2401 (3) DS2411 (3) DS1990A (3)
158
159   Memory
160       DS1982  (3)  DS1985  (3)  DS1986  (3)  DS1991 (3) DS1992 (3) DS1993 (3)
161       DS1995 (3) DS1996 (3) DS2430A (3) DS2431  (3)  DS2433  (3)  DS2502  (3)
162       DS2506 (3) DS28E04 (3) DS28EC20 (3)
163
164   Switches
165       DS2405 (3) DS2406 (3) DS2408 (3) DS2409 (3) DS2413 (3) DS28EA00 (3)
166
167   Temperature
168       DS1822  (3)  DS1825  (3)  DS1820 (3) DS18B20 (3) DS18S20 (3) DS1920 (3)
169       DS1921 (3) DS1821 (3) DS28EA00 (3) DS28E04 (3) EDS0064 (3) EDS0065  (3)
170       EDS0066  (3)  EDS0067  (3) EDS0068 (3) EDS0071 (3) EDS0072 (3) MAX31826
171       (3)
172
173   Humidity
174       DS1922 (3) DS2438 (3) EDS0065 (3) EDS0068 (3)
175
176   Voltage
177       DS2450 (3)
178
179   Resistance
180       DS2890 (3)
181
182   Multifunction (current, voltage, temperature)
183       DS2436 (3) DS2437 (3) DS2438 (3)  DS2751  (3)  DS2755  (3)  DS2756  (3)
184       DS2760 (3) DS2770 (3) DS2780 (3) DS2781 (3) DS2788 (3) DS2784 (3)
185
186   Counter
187       DS2423 (3)
188
189   LCD Screen
190       LCD (3) DS2408 (3)
191
192   Crypto
193       DS1977 (3)
194
195   Pressure
196       DS2406 (3) TAI8570 (3) EDS0066 (3) EDS0068 (3)
197
198   Moisture
199       EEEF (3) DS2438 (3)
200

AVAILABILITY

202       http://www.owfs.org
203

AUTHOR

205       Paul Alfille (paul.alfille@gmail.com)
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209OWFS Manpage                         2003                            DS1821(3)
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