27-06-2012, 10:55 AM
Seminar on iButton Standards
[attachment=25688]
. Introduction
This book defines mechanical, electrical, and logical iButton standards. As with any standard, there are ways to ensure that an application meets the standards. For applications in full compliance with the standard, Dallas Semiconductor will authorize the use of Certified Dallas TouchTM labels, which can be placed on a company’s products.
Touch Validator
The Touch Validator is a Touch Pen with the addition of validation firmware executed by the internal processor. The Touch Validator checks timing characteristics,ROM contents, and the structure of data stored in the nonvolatile RAM of a Memory iButton. Beyond that, it runs a diagnostic on the integrity of the file structure (not applicable for the DS1990A and DS1991). If any deviation from the standards is detected, the complete RAM contents are copied for additional analysis by a PC. This mode of operation allows fast ”go/no go” checking and validation directly at the location of the iButton. For information on Validator firmware, please contact Dallas Semiconductor.
Default Data Structure
Since it is an official standard, the validation firmware will also accept the Default Data Structure, which is actually the predecessor of the file structure described in Chapter 7. The Default Data Structure has advantages in applications where a sophisticated directory structure is not required. It saves some space since one page can contain up to 32 bytes of application data instead of 28; it also simplifies the software, which will save ROM code of single–chip microcontrollers. In contrast to the Extended File Structure, however, the Default Data Structure does not support multiple files in the same device, CRC–checked reading of single memory pages, scattered continuation pages, and data records of more than 508 bytes. The default data structure assumes that only one unnamed file will be stored in an iButton. It defines that the first one or two bytes on page 0 contain the length of the data record. If the data record is longer than 254 bytes, then the first byte of page 0 is 255, and the second byte is deployed to store the number of bytes exceeding 255.
Chapter Summary
The Touch Validator is a device that checks whether an iButton Application is in compliance with the iButton standards as described in this book. In addition to the iButton File Structure described in Chapter 7, the Default Data Structure is accepted as standard for simple applications.
PRODUCT OVERVIEW
DEVICES
A MicroCans:
The sections below explain the different versions ofiButton MicroCans.Tablegives a complete overview of the product family.
DS1990A Serial Number iButton:
The simplest iButton is the DS1990A,a factoryprogrammed ROM. Since the information is stored in lasercut polysilicon links (not as charge on gates or as statesof flipflops), the DS1990A needs no energy to retaindata. Furthermore,almost no energy is requiredforoperation. The DS1990A uses the voltage of the dataline and stores a minimum of charge internally to maintain operation during the presence pulse and the lowtime of any time slot during a read operation. Figure shows how data is organized within the DS1990A.
The first byte to be transmitted out of the ROM is thefamilycode.After this,the guaranteed unique serialnumber follows, least significant byte first. The last byteof signature of the first 7 bytes. It allows fast checking ofthe completecommunication sequence. If the CRC calculated by the reading master matches the CRC readfrom the device, the reading was completely correct.This is one of the reasons why iButtons don’t requirestableelectrical contacts.Because of its design and the strict controlof themanufacturing process,the DS1990A is a unique electronic identifierthat is impractical to be counterfeited.Itis appropriate for applications where absolute identification is required.
DS1991 MULTIKEY IBUTTON:
DS1991 MultiKeyiButton like the DS1990A,the DS1991 incorporates a serialnumber with family code and CRC. To this it adds a 64 byte nonvolatile scratchpad RAM, and three independent password secured nonvolatile RAM areas of48 bytes each, called subkeys. For every secured RAMarea there is also a public identification field of eight bytes.
[attachment=25688]
. Introduction
This book defines mechanical, electrical, and logical iButton standards. As with any standard, there are ways to ensure that an application meets the standards. For applications in full compliance with the standard, Dallas Semiconductor will authorize the use of Certified Dallas TouchTM labels, which can be placed on a company’s products.
Touch Validator
The Touch Validator is a Touch Pen with the addition of validation firmware executed by the internal processor. The Touch Validator checks timing characteristics,ROM contents, and the structure of data stored in the nonvolatile RAM of a Memory iButton. Beyond that, it runs a diagnostic on the integrity of the file structure (not applicable for the DS1990A and DS1991). If any deviation from the standards is detected, the complete RAM contents are copied for additional analysis by a PC. This mode of operation allows fast ”go/no go” checking and validation directly at the location of the iButton. For information on Validator firmware, please contact Dallas Semiconductor.
Default Data Structure
Since it is an official standard, the validation firmware will also accept the Default Data Structure, which is actually the predecessor of the file structure described in Chapter 7. The Default Data Structure has advantages in applications where a sophisticated directory structure is not required. It saves some space since one page can contain up to 32 bytes of application data instead of 28; it also simplifies the software, which will save ROM code of single–chip microcontrollers. In contrast to the Extended File Structure, however, the Default Data Structure does not support multiple files in the same device, CRC–checked reading of single memory pages, scattered continuation pages, and data records of more than 508 bytes. The default data structure assumes that only one unnamed file will be stored in an iButton. It defines that the first one or two bytes on page 0 contain the length of the data record. If the data record is longer than 254 bytes, then the first byte of page 0 is 255, and the second byte is deployed to store the number of bytes exceeding 255.
Chapter Summary
The Touch Validator is a device that checks whether an iButton Application is in compliance with the iButton standards as described in this book. In addition to the iButton File Structure described in Chapter 7, the Default Data Structure is accepted as standard for simple applications.
PRODUCT OVERVIEW
DEVICES
A MicroCans:
The sections below explain the different versions ofiButton MicroCans.Tablegives a complete overview of the product family.
DS1990A Serial Number iButton:
The simplest iButton is the DS1990A,a factoryprogrammed ROM. Since the information is stored in lasercut polysilicon links (not as charge on gates or as statesof flipflops), the DS1990A needs no energy to retaindata. Furthermore,almost no energy is requiredforoperation. The DS1990A uses the voltage of the dataline and stores a minimum of charge internally to maintain operation during the presence pulse and the lowtime of any time slot during a read operation. Figure shows how data is organized within the DS1990A.
The first byte to be transmitted out of the ROM is thefamilycode.After this,the guaranteed unique serialnumber follows, least significant byte first. The last byteof signature of the first 7 bytes. It allows fast checking ofthe completecommunication sequence. If the CRC calculated by the reading master matches the CRC readfrom the device, the reading was completely correct.This is one of the reasons why iButtons don’t requirestableelectrical contacts.Because of its design and the strict controlof themanufacturing process,the DS1990A is a unique electronic identifierthat is impractical to be counterfeited.Itis appropriate for applications where absolute identification is required.
DS1991 MULTIKEY IBUTTON:
DS1991 MultiKeyiButton like the DS1990A,the DS1991 incorporates a serialnumber with family code and CRC. To this it adds a 64 byte nonvolatile scratchpad RAM, and three independent password secured nonvolatile RAM areas of48 bytes each, called subkeys. For every secured RAMarea there is also a public identification field of eight bytes.