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Features
2,
4, 8, 16, 32 or 64 k bytes of non-volatile
EEPROM
Rugged construction to military standards
Asynchronous UART/RS232 compatible
Unique 32 bit serial number
Secure 64 bit password
Selective memory write protection
16 bit CRC error correction
Oxley e-tags are contact memory tags containing up-to 64 k bytes
of EEPROM non-volatile memory housed in small rugged metal cans.
e-tags are intended for permanent attachment to host assets in order
store any kind of digital information relevant to the asset, creating
a secure portable micro-database co-resident with the asset itself.
When
interfaced to a host controller an e-tag is capable of having its
memory read-from or written-to virtually an unlimited number of
times. When disconnected from a host controller the data stored
can be retained for over 100 years. e-tags are passive containing
no battery or internal power source to retain data.
Physical
protocol
Physical signalling between e-tag and a host controller uses asynchronous
serial data compatible with common integrated circuit UARTs (universal
asynchronous receiver transmitter) operating in 'simplex' bi-directional
mode at 57.6k bits per second.
Unique
serial number
Each e-tag has a unique 32 bit serial number stored in ROM which
cannot be altered or erased but can be read by a host device.
Secure
password protection
e-tag contact memory has a true password protection function whereby
a 64 bit password can be set and stored securely in EEPROM. If enabled,
the password must be supplied, for each tag, to access the data.
Prior to a password being set a host device can access full read/write
functionality. Once a password has been set on an e-tag the host
must provide a matching password before further reading or writing
of EEPROM is permitted. A previously set password can be cleared
by supplying a matching existing password.
Memory
write protection
Areas of EEPROM can be permanently locked preventing further writing
of data but allowing continued reading of the data from this area.
This can be used to lock just a few bytes of EEPROM or the whole
e-tag. Once a lock has been set it cannot be reversed. A lock can
be extended allowing data to be protected as it is added.
Error
correction
All host communications to and from an e-tag contain a 16 bit cyclic
redundancy check (CRC) stored within the communication packet. For
command messages sent by the host controller, the host must calculate
the CRC value. On receipt of the command packet the e-tag will perform
its own CRC calculation and compare it to the contents of the received
packet CRC value. If the two do not match then an error code will
be returned by the e-tag.
Conversely,
for response messages the e-tag calculates the CRC and places it
in the response packet. On receipt of the response packet the host
should perform its own CRC calculation and compare it to the contents
of the received packet CRC. If the two do not match then it is the
responsibility of the host to take appropriate action.
A detailed
interface specification is available to integrators. Go to software
integrators pages.
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