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iButton Memory Overview

In a sense, all iButton® devices are memory buttons because there are no iButton devices without memory. Therefore, the concept of a mobile memory chip that communicates by touch remains fundamental to all iButton products. As the iButton family has grown, however, memory-only iButton devices are now distinguished from iButton products with extended capabilities such as a microprocessor, clock, and/or environmental sensors. Memory-only iButton devices come in these different types to allow you to pick the right device for your specific application.
All memory-only iButton devices have these characteristics:
  • Unique and unalterable factory-lasered address
  • Low-cost, low-power 1-Wire® interface
  • Ability to operate as mobile database, in either standalone or networked application designs
Memory iButton devices can be divided into the following different categories:
The Address-Only iButton device is our DS1990A iButton serial number device and is our basis model. It contains 64bits of Read-Only Memory (ROM) and is used in many different applications such as:
  • Access Control as a Key
  • Route Compliance as a Location Identifier
  • Inspection and Maintenance for Equipment Identification
NV RAM iButton devices are read/write devices and are available in sizes from 1K bits to 64K bits. They are used for applications that need data updated on a frequent basis. The memory is capable of being rewritten millions of times. In addition, the onboard lithium energy source is ideally suited for the typical iButton environment where electrical contact can be intermittent. Memory updates, once initiated, will always be completed because the power to finish the transfer is supplied by the lithium cell, not the reader/writer.
EPROM iButton devices are Add Only devices (write once read many). They are available in sizes from 1K bits to 64K bits and allow you to write to the button until the memory is full. The data can not be erased after it has been written to the button. EPROM iButton devices are useful in application where the data needs to be permanent. They also give you the ability to write blocks of data to the device incrementally to build and store a record of activity over a period of time.
Uniqueware iButton products are EPROM devices that are only available preprogrammed with customer-specific and write-protected data. UniqueWare data fills at least one but no more than the first four pages of a device, depending on the length of the customer-supplied data.
EEPROM iButton products are read/write devices and are available in sizes from 256 bits to 32K bytes. They are used for applications that need data updated on a less frequent basis than NVRAM type applications, but are usable for over 10 years. EEPROM iButton devices are also less expensive than NVRAM devices, but have a lower write cycle limit.