NAME¶
DS1825, MAX31826 - Programmable Resolution 1-Wire Digital Thermometer
with ID, Digital Temperature Sensor with 1Kb Lockable EEPROM
- MAX31850 MAX31851
- - Cold-Junction Compensated Thermocouple
SYNOPSIS¶
Thermometer with hardware address pins (DS1825)¶
3B [.]XXXXXXXXXXXX[XX][/[
fasttemp |
temperature |
temperature9 |
temperature10 |
temperature11 |
temperature12 |
power |
prog_addr |
temphigh |
templow |
address |
crc8 |
id |
locator |
r_address |
r_id |
r_locator |
type ]]
Digital Temperature Sensor with 1Kb Lockable EEPROM (MAX31826)¶
3B [.]XXXXXXXXXXXX[XX][/[
temperature |
power |
memory |
pages/page.[0-15|ALL] |
prog_addr |
address |
crc8 |
id |
locator |
r_address |
r_id |
r_locator |
type ]]
Cold-Junction Compensated Thermocouple (MAX31850 and MAX31851)¶
3B [.]XXXXXXXXXXXX[XX][/[
temperature |
thermocouple |
fault |
open_circuit |
ground_short |
vdd_short |
power |
prog_addr |
address |
crc8 |
id |
locator |
r_address |
r_id |
r_locator |
type ]]
FAMILY CODE¶
3B
SPECIAL PROPERTIES¶
power¶
read-only,yes-no
Is the chip powered externally (=1) or from the parasitically from the data bus
(=0)?
prog_addr¶
read-only, 0-15
A distiguishing feature of the
DS1825 (3) is the ability to set hardware
pins for an address (0-15). This is an alternative to the unique 64-bit
address that is set in the factory.
temperature¶
read-only, floating point
Measured temperature with 12 bit resolution.
For the
MAX31850 MAX 31851 this is the
cold-junction temperature
-- the temperature at the chip. See
thermocouple
temperature9 temperature10 temperature11 temperature12¶
read-only, floating point (
DS1825 only)
Measured temperature at 9 to 12 bit resolution. There is a tradeoff of time
versus accuracy in the temperature measurement.
The
MAX31826 MAX31850 MAX31851 measure all temperatures at 12 bit
resoltion and will return that resolution to all the possible temperature
properties.
fasttemp¶
read-only, floating point
Equivalent to
temperature9
thermocouple¶
read-only, floating point (
MAX31850 MAX31851 only)
Measured temperature of the thermocouple at 16bit resolution. Cold-junction
temperature compensated.
The actual thermocouple type used is set by the selected chip type, and is not
discoverable in software.
TEMPERATURE ALARM LIMITS¶
When the device exceeds either
temphigh or
templow temperature
threshold the device is in the alarm state, and will appear in the alarm
directory. This provides an easy way to poll for temperatures that are unsafe,
especially if
simultaneous temperature conversion is done.
Units for the temperature alarms are in the same
temperature scale that
was set for
temperature measurements.
Temperature thresholds are stored in non-volatile memory and persist until
changed, even if power is lost.
temphigh¶
read-write, integer
Shows or sets the lower limit for the high temperature alarm state.
templow¶
read-write, integer
Shows or sets the upper limit for the low temperature alarm state.
The
MAX31826 does NOT have temperature thresholds and temperature alarm.
MEMORY¶
Only the
MAX31826 supports memory functions.
pages/page.0 .. pages/page.15 pages/page.ALL¶
read/write, binary
EEPROM memory pages of 8 bytes each. See the datasheet about locking contents.
memory¶
read/write, binary
EEPROM memory of 128 bytes. See the datasheet about locking contents.
FAULT REPORTING¶
Only the
MAX31850 MAX31851 supports fault reporting.
fault¶
read-only, yes-no
Fault in last thermocouple conversion
open_circuit¶
read-only, yes-no
Thermocouple leads disconnected.
ground_short¶
read-only, yes-no
Thermocouple lead shorted to ground.
vdd_short¶
read-only, yes-no
Thermocouple lead shorted to supply voltage.
STANDARD PROPERTIES¶
address¶
r_address¶
read-only, ascii
The entire 64-bit unique ID. Given as upper case hexidecimal digits (0-9A-F).
address starts with the
family code
r address is the
address in reverse order, which is often used in
other applications and labeling.
crc8¶
read-only, ascii
The 8-bit error correction portion. Uses cyclic redundancy check. Computed from
the preceding 56 bits of the unique ID number. Given as upper case hexidecimal
digits (0-9A-F).
family¶
read-only, ascii
The 8-bit family code. Unique to each
type of device. Given as upper case
hexidecimal digits (0-9A-F).
r_id¶
read-only, ascii
The 48-bit middle portion of the unique ID number. Does not include the family
code or CRC. Given as upper case hexidecimal digits (0-9A-F).
r id is the
id in reverse order, which is often used in other
applications and labeling.
locator¶
r_locator¶
read-only, ascii
Uses an extension of the 1-wire design from iButtonLink company that associated
1-wire physical connections with a unique 1-wire code. If the connection is
behind a
Link Locator the
locator will show a unique 8-byte number
(16 character hexidecimal) starting with family code FE.
If no
Link Locator is between the device and the master, the
locator field will be all FF.
r locator is the
locator in reverse order.
present (DEPRECATED)¶
read-only, yes-no
Is the device currently
present on the 1-wire bus?
type¶
read-only, ascii
Part name assigned by Dallas Semi. E.g.
DS2401 Alternative packaging
(iButton vs chip) will not be distiguished.
DESCRIPTION¶
1-Wire¶
1-wire is a wiring protocol and series of devices designed and
manufactured by Dallas Semiconductor, Inc. The bus is a low-power low-speed
low-connector scheme where the data line can also provide power.
Each device is uniquely and unalterably numbered during manufacture. There are a
wide variety of devices, including memory, sensors (humidity, temperature,
voltage, contact, current), switches, timers and data loggers. More complex
devices (like thermocouple sensors) can be built with these basic devices.
There are also 1-wire devices that have encryption included.
The 1-wire scheme uses a single
bus master and multiple
slaves on
the same wire. The bus master initiates all communication. The slaves can be
individually discovered and addressed using their unique ID.
Bus masters come in a variety of configurations including serial, parallel, i2c,
network or USB adapters.
OWFS design¶
OWFS is a suite of programs that designed to make the 1-wire bus and its
devices easily accessible. The underlying priciple is to create a virtual
filesystem, with the unique ID being the directory, and the individual
properties of the device are represented as simple files that can be read and
written.
Details of the individual slave or master design are hidden behind a consistent
interface. The goal is to provide an easy set of tools for a software designer
to create monitoring or control applications. There are some performance
enhancements in the implementation, including data caching, parallel access to
bus masters, and aggregation of device communication. Still the fundemental
goal has been ease of use, flexibility and correctness rather than speed.
DS1825¶
The
DS1825 (3) is one of several available 1-wire temperature sensors.
Alternatives are the
DS18S20 (3), DS18B20 (3), and
DS1822
(3) as well as temperature/voltage measurements in the
DS2436 (3)
and
DS2438 (3). For truly versatile temperature measurements, see the
protean
DS1921 (3) Thermachron (3).
The
DS1825 (3) can select between 4 resolutionsspanning the
fastest/roughest and slowest/best.
MAX31826¶
The
MAX31826 shares a family code with the
DS1825 but has
differences in some of its functions.
The
MAX31826 has 128 btes of EEPROM memory (as 16 pages of 8 bytes) while
the
DS1825 has no memory available.
The
MAX31826 measures temperature at 12 bit resolution as fast as the
DS1825's lowest resolution (and always uses 12-bit resolution). On the
other hand it has no temperature thresholds or alarm function.
ADDRESSING¶
All 1-wire devices are factory assigned a unique 64-bit address. This address is
of the form:
- Family Code
- 8 bits
- Address
- 48 bits
- CRC
- 8 bits
Addressing under OWFS is in hexidecimal, of form:
- 01.123456789ABC
where
01 is an example 8-bit family code, and
12345678ABC is an
example 48 bit address.
The dot is optional, and the CRC code can included. If included, it must be
correct.
Both the
MAX31826 and the
DS1825 allow hardware selection of part
of the address, which can assist selecting between chips is some circuit
designs.
DATASHEET¶
- DS1825
- http://pdfserv.maxim-ic.com/en/ds/DS1825.pdf
- MAX31826
- http://datasheets.maxim-ic.com/en/ds/MAX31826.pdf
SEE ALSO¶
Programs¶
owfs (1) owhttpd (1) owftpd (1) owserver (1) owdir (1) owread (1)
owwrite (1) owpresent (1) owtap (1)
Configuration and testing¶
owfs (5) owtap (1) owmon (1)
Language bindings¶
owtcl (3) owperl (3) owcapi (3)
Clocks¶
DS1427 (3) DS1904(3) DS1994 (3) DS2404 (3) DS2404S (3) DS2415 (3) DS2417
(3)
DS2401 (3) DS2411 (3) DS1990A (3)
Memory¶
DS1982 (3) DS1985 (3) DS1986 (3) DS1991 (3) DS1992 (3) DS1993 (3) DS1995 (3)
DS1996 (3) DS2430A (3) DS2431 (3) DS2433 (3) DS2502 (3) DS2506 (3) DS28E04 (3)
DS28EC20 (3)
Switches¶
DS2405 (3) DS2406 (3) DS2408 (3) DS2409 (3) DS2413 (3) DS28EA00 (3)
Temperature¶
DS1822 (3) DS1825 (3) DS1820 (3) DS18B20 (3) DS18S20 (3) DS1920 (3) DS1921
(3) DS1821 (3) DS28EA00 (3) DS28E04 (3) EDS0064 (3) EDS0065 (3) EDS0066 (3)
EDS0067 (3) EDS0068 (3) EDS0071 (3) EDS0072 (3) MAX31826 (3)
Humidity¶
DS1922 (3) DS2438 (3) EDS0065 (3) EDS0068 (3)
Voltage¶
DS2450 (3)
Resistance¶
DS2890 (3)
Multifunction (current, voltage, temperature)¶
DS2436 (3) DS2437 (3) DS2438 (3) DS2751 (3) DS2755 (3) DS2756 (3) DS2760 (3)
DS2770 (3) DS2780 (3) DS2781 (3) DS2788 (3) DS2784 (3)
Counter¶
DS2423 (3)
LCD Screen¶
LCD (3) DS2408 (3)
Crypto¶
DS1977 (3)
Pressure¶
DS2406 (3) TAI8570 EDS0066 (3) EDS0068 (3)
Moisture¶
EEEF (3) DS2438 (3)
AVAILABILITY¶
http://www.owfs.org
AUTHOR¶
Paul Alfille (paul.alfille@gmail.com)