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EconoRAM time chip
Dual port memory plus time
4k plus time iButton
Time iButton


Real time clock, 4kbit memory. 3-wire interface, too.

04.XXXXXXXXXXXX / alarm | auto | cycle | date | delay | interval | memory | pages/page.[0-15|ALL] | readonly/[memory|clock|cycle|interval] | memory | pages/page.[0-15|ALL] | readonly/[memory|clock|cycle|interval] | running | set_alarm | start | trigger/[cycle,date,interval,udate,uinterval] | udate | uinterval | address | crc8 | id | locator | r_address | r_id | r_locator | type

84.XXXXXXXXXXXX / alarm | auto | cycle | date | delay | interval | memory | pages/page.[0-15|ALL] | readonly/[memory|clock|cycle|interval] | running | set_alarm | start | trigger/[cycle,date,interval,udate,uinterval] | udate | uinterval | address | crc8 | id | present | type

Family Code

  1. DS2404 DS1994
  2. DS1427 DS2404S

Special Properties


read-write, unsigned integer (0-111)
Alarm state of the DS2404 (3) triggered by time or counter events. Reading the alarm state clears the alarm.
The alarm value is of the form CIR, where:
cycle counter alarm
0 no
1 yes
interval timer alarm
0 no
1 yes
real-time clock alarm
0 no
1 yes


read-write, yes-no
Flag for mode of interval counter operation. 0=manual 1=auto
See the datasheet for details.


read-write, ascii
26 character date representation of the udate value. Increments once per second while running
Actual internal representation has higher precision.
Cannot be altered if readonly/clock is set.
Setting date to a null string will put the current system time.
Accepted date formats are:
Sat[urday] March 12 12:23:59 2001

Apr[il] 4 9:34:56 2002

3/23/04 23:34:57

current locale setting (your system’s format)


read-write, yes-no
Flag for adding a delay to cycle counter. 0=short 1-long
See the datasheet under "IDEL" for details.


read-write, date
Interval timer value, represented as a date string. More typically will be used as uinterval to read the actual elapsed seconds.


read-write, binary
512 bytes of memory. The readonly/memory flag prevents further change.

pages/page.0 ... pages/page.15 pages/page.ALL

read-write, yes-no
Memory is split into 16 pages of 32 bytes each. The readonly/memory flag prevents further change. ALL is an aggregate of the pages. Each page is accessed sequentially.


read-write, yes-no
Permanently protect part of the chip’s function from alteration.
page.X and memory
date and udate


read-write, yes-no
State of the clock. 0=off 1=running.


read-write, unsigned integer (0-111)
Which of the alarm triggers are enabled in the DS2404 (3)
The set_alarm value is of the form CIR, where:
cycle counter alarm
0 no
1 yes
interval timer alarm
0 no
1 yes
real-time clock alarm
0 no
1 yes


read-write, yes-no
Flag for starting the interval counter operation if not in auto mode. 0=stop 1=start
See the datasheet for details.


Target value that will trigger the alarm if the corresponding set_alarm field is set.
The format is the same as the similarly named field (i.e. date for trigger/date )


read-write, unsigned integer
Time represented as a number. udate increments once per second, while running is on.
Usually set to unix time standard: number of seconds since Jan 1, 1970. The date field will be the unix representation of udate and setting either will change the other.


read-write, unsigned interval
Similar to the udate field, except corresponds to the interval value.

Standard Properties



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.


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).


read-only, ascii
The 8-bit family code. Unique to each type of device. Given as upper case hexidecimal digits (0-9A-F).



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.



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?


read-only, ascii
Part name assigned by Dallas Semi. E.g. DS2401 Alternative packaging (iButton vs chip) will not be distiguished.


None implemented.



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.

Ds1427 Ds1994 Ds2404 Ds2404s

The DS1427 (3) , DS1994 (3) , DS2404 (3) , and DS2404S (3) family of 1-wire devices includes clock functions, with timers, memory, counters and alarms. It is possible to write-protect regians of memory. Uses include software or hardware timing and control.


Both the DS2404 (3) and DS2404S (3) have 1-wire and 3-wire interfaces, which might be useful for transferring data between the 2 buses. They act as a passive slave to both busses. The DS2404 (3) and DS2404S (3) require an external source of power and an external crystal. They also offer a reset and 1HZ clock pin.


Both the DS1427 and DS1994 offer the memory, alarms, and clock function in iButton format. Because the iButton is a complete sealed package, battery and crystal are internal. Everything is access via the 1-wire interface.


All 1-wire devices are factory assigned a unique 64-bit address. This address is of the form:
Family Code
8 bits
48 bits
8 bits

Addressing under OWFS is in hexidecimal, of form:

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.


See Also


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)


DS1427 (3) DS1904(3) DS1994 (3) DS2404 (3) DS2404S (3) DS2415 (3) DS2417 (3)


DS2401 (3) DS2411 (3) DS1990A (3)


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)


DS2405 (3) DS2406 (3) DS2408 (3) DS2409 (3) DS2413 (3) DS28EA00 (3)


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)


DS1922 (3) DS2438 (3) EDS0065 (3) EDS0068 (3)


DS2450 (3)


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)


DS2423 (3)

LCD Screen

LCD (3) DS2408 (3)


DS1977 (3)


DS2406 (3) TAI8570 EDS0066 (3) EDS0068 (3)


EEEF (3) DS2438 (3)



Paul Alfille (

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