SYNOPSIS
Voltage * 4 and Memory.
20 [.]XXXXXXXXXXXX[XX][/[ PIO.[A-D|ALL] | volt.[A-D|ALL] | volt2.[A-D|ALL] ]]
20 [.]XXXXXXXXXXXX[XX][/[ 8bit/volt.[A-D|ALL] | 8bit/volt2.[A-D|ALL] ]]
20 [.]XXXXXXXXXXXX[XX][/[ memory | pages/page.[0-3|ALL] | power ]
20 [.]XXXXXXXXXXXX[XX][/[ alarm/high.[A-D|ALL] | alarm/low.[A-D|ALL] | set_alarm/high.[A-D|ALL] | set_alarm/low.[A-D|ALL] | set_alarm/unset | set_alarm/volthigh.[A-D|ALL] | set_alarm/volt2high.[A-D|ALL] | set_alarm/voltlow.[A-D|ALL] | set_alarm/volt2low.[A-D|ALL] ]
20 [.]XXXXXXXXXXXX[XX][/[ address | crc8 | id | locator | r_address | r_id | r_locator | type ]]
CO2 sensor
20 [.]XXXXXXXXXXXX[XX][/[ CO2/ppm | CO2/power | CO2/status ]
FAMILY CODE
20
SPECIAL PROPERTIES
alarm/high.A ... alarm/high.D alarm.high.ALL
alarm/high.A ... alarm/high.D alarm.high.ALL
read-write, binaryThe alarm state of the voltage channel. The alarm state is set one of two ways:
- voltage conversion
- Whenever the DS2450 measures a voltage on a channel, that voltage is compared to the high and low limits set_alarm/volthigh and/or set_alarm/voltlow and if the alarm is enabled set_alarm/high and/or set_alarm/low the corresponding flag is set in alarm/high and/or alarm/low
- manual set
- The flag can be set by a direct write to alarm/high or alarm/low
memory
read-write, binary32 bytes of data. Much has special implications. See the datasheet.
pages/page.0 ... pages/page.3 pages/page.ALL
read-write, binaryMemory is split into 4 pages of 8 bytes each. Mostly for reading and setting device properties. See the datasheet for details.
ALL is an aggregate of the pages. Each page is accessed sequentially.
PIO.A ... PIO.D PIO.ALL
read-write, yes-noPins used for digital control. 1 turns the switch on (conducting). 0 turns the switch off (non-conducting).
Control is specifically enabled. Reading volt will turn off this control.
ALL is an aggregate of the voltages. Readings are made separately.
power
read-write, yes-noIs the DS2450 externally powered? (As opposed to parasitically powered from the data line).
The analog A/D will be kept on continuously. And the bus will be released during a conversion allowing other devices to communicate.
Set true (1) only if Vcc powered (not parasitically powered). Unfortunately, the DS2450 cannot sense it's powered state. This flag must be explicitly written, and thus is a potential source of error if incorrectly set.
It is always safe to leave power set to the default 0 (off) state.
set_alarm/high.A ... set_alarm/high.D set_alarm/high.ALL
set_alarm/low.A ... set_alarm/low.D set_alarm/low.ALL
read-write, yes-noEnabled status of the voltage threshold. 1 is on. 0 is off.
set_alarm/volthigh.A ... set_alarm/volthigh.D set_alarm/volthigh.ALL
set_alarm/volt2high.A ... set_alarm/volt2high.D set_alarm/volt2high.ALL
set_alarm/voltlow.A ... set_alarm/voltlow.D set_alarm/voltlow.ALL
set_alarm/volt2low.A ... set_alarm/volt2low.D set_alarm/volt2low.ALL
read-write, floating pointThe upper or lower limit for the voltage measured before triggering an alarm.
Note that the alarm must be enabled alarm/high or alarm.low and an actual reading must be requested volt for the alarm state to actually be set. The alarm state can be sensed at alarm/high and alarm/low
set_alarm/unset
read-write, yes-noStatus of the power-on-reset (POR) flag.
The POR is set when the DS2450 is first powered up, and will match the alarm state until explicitly cleared. (By writing 0 to it).
The purpose of the POR is to alert the user that the chip is not yet fully configured, especially alarm thresholds and enabling.
volt.A ... volt.D volt.ALL
8bit/volt.A ... 8bit/volt.D 8bit/volt.ALL
read-only, floating pointVoltage read, 16 bit resolution (or 8 bit for the 8bit directory). Range 0 - 5.10V.
Output ( PIO ) is specifically disabled.
ALL is an aggregate of the voltages. Readings are made separately.
volt2.A ... volt2.D volt2.ALL
8bit/volt2.A ... 8bit/volt2.D 8bit/volt2.ALL
read-only, floating pointVoltage read, 16 bit resolution (or 8 bit for the 8bit directory). Range 0 - 2.55V.
Output ( PIO ) is specifically disabled.
ALL is an aggregate of the voltages. Readings are made separately.
CO2 (Carbon Dioxide) SENSOR PROPERTIES
The CO2 sensor is a device constructed from a SenseAir K30 and a DS2450CO2/power
read-only, floating pointSupply voltage to the CO2 sensor (should be around 5V)
CO2/ppm
read-only, unsignedCO2 level in ppm (parts per million). Range 0-5000.
CO2/status
read-only, yes-noIs the internal voltage correct (around 3.2V)?
STANDARD PROPERTIES
address
r_address
read-only, asciiThe entire 64-bit unique ID. Given as upper case hexadecimal 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, asciiThe 8-bit error correction portion. Uses cyclic redundancy check. Computed from the preceding 56 bits of the unique ID number. Given as upper case hexadecimal digits (0-9A-F).
family
read-only, asciiThe 8-bit family code. Unique to each type of device. Given as upper case hexadecimal digits (0-9A-F).
id
r_id
read-only, asciiThe 48-bit middle portion of the unique ID number. Does not include the family code or CRC. Given as upper case hexadecimal 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, asciiUses 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 hexadecimal) 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-noIs the device currently present on the 1-wire bus?
type
read-only, asciiPart name assigned by Dallas Semi. E.g. DS2401 Alternative packaging (iButton vs chip) will not be distiguished.
ALARMS
None.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 principle 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.
DS2450
The DS2450 (3) is a (supposedly) high resolution A/D converter with 4 channels. Actual resolutin is reporterd to be 8 bits. The channels can also function as switches. Voltage sensing (with temperature and current, but sometimes restricted voltrage ranges) can also be obtained with the DS2436 , DS2438 and DS276xADDRESSING
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 hexadecimal, 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.