1DS1821(3) One-Wire File System DS1821(3)
2
6 DS1821 - Programmable Digital Thermostat and Thermometer
7
9 Thermostat.
10 thermostat [/[ temperature | temphigh | templow | temphighflag | tem‐
12 plowflag | thermostatmode | polarity | 1shot ]]
13
15 none
16
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 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 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 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 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 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
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 Units for the temperature alarms are in the same temperature scale that
71 was set for temperature measurements.
72 Temperature thresholds are stored in non-volatile memory and persist
74 until changed, even if power is lost.
75 temphigh
77 read-write, integer
78 Shows or sets the lower limit for the high temperature alarm state.
79 templow
81 read-write, integer
82 Shows or sets the upper limit for the low temperature alarm state.
83
85 type
86 read-only, ascii
87 Chip type: DS1821
88
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 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 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 Bus masters come in a variety of configurations including serial, par‐
107 allel, i2c, network or USB adapters.
108 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 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 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.
131
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
139 http://pdfserv.maxim-ic.com/en/ds/DS1821.pdf
140
142 Programs
143 owfs (1) owhttpd (1) owftpd (1) owserver (1) owdir (1) owread (1)
144 owwrite (1) owpresent (1) owtap (1)
145 Configuration and testing
147 owfs (5) owtap (1) owmon (1)
148 Language bindings
150 owtcl (3) owperl (3) owcapi (3)
151 Clocks
153 DS1427 (3) DS1904 (3) DS1994 (3) DS2404 (3) DS2404S (3) DS2415 (3)
154 DS2417 (3)
155 ID
157 DS2401 (3) DS2411 (3) DS1990A (3)
158 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 Switches
165 DS2405 (3) DS2406 (3) DS2408 (3) DS2409 (3) DS2413 (3) DS28EA00 (3)
166 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 [1m(3)
172 Humidity
174 DS1922 (3) DS2438 (3) EDS0065 (3) EDS0068 (3)
175 Voltage
177 DS2450 (3)
178 Resistance
180 DS2890 (3)
181 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 Counter
187 DS2423 (3)
188 LCD Screen
190 LCD (3) DS2408 (3)
191 Crypto
193 DS1977 (3)
194 Pressure
196 DS2406 (3) TAI8570 (3) EDS0066 (3) EDS0068 (3)
197 Moisture
199 EEEF (3) DS2438 (3)
200
202 http://www.owfs.org
203
205 Paul Alfille (paul.alfille@gmail.com)
206OWFS Manpage 2003 DS1821(3)