DS5002FP_1 Datasheet, PDF (10/29 Pages) Dallas Semiconductor – Secure Microprocessor Chip

DS5002FP
this action. In addition, power is momentarily removed from the byte-wide bus interface including the
V_CCO pin, resulting in the loss of data in external RAM.
TOP LAYER COATING
The DS5002FPM is provided with a special top-layer coating that is designed to prevent a probe attack.
This coating is implemented with second-layer metal added through special processing of the
microcontroller die. This additional layer is not a simple sheet of metal, but rather a complex layout that
is interwoven with power and ground, which are in turn connected to logic for the Encryption Key and
the Security Lock. As a result, any attempt to remove the layer or probe through it will result in the
erasure of the Security Lock and/or the loss of Encryption Key bits.
BOOTSTRAP LOADING
Initial loading of application software into the DS5002FP is performed by firmware within the on-chip
Bootstrap Loader communicating with a PC via the on-chip serial port in a manner which is almost
identical to that for the DS5001FP. The user should consult the DS5001FP data sheet as a basis of
operational characteristics of this firmware. Certain differences in loading procedure exist in order to
support the security feature. These differences are documented below. Table 1 summarizes the
commands accepted by the bootstrap loader.
When the Bootstrap Loader is invoked, portions of the 128-byte scratchpad RAM area are automatically
overwritten with zeroes, and then used for variable storage for the bootstrap firmware. Also, a set of 8
bytes are generated using the random number generator circuitry and are saved as a potential word for the
64-bit Encryption Key.
Any read or write operation to the DS5002FP’s external program/data SRAM can only take place if the
Security Lock bit is in a cleared state. Therefore, the first step which is taken in the loading of a program
should be the clearing of the Security Lock bit through the “U” command.
10 of 29