User Manual

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16 JN-DS-JN5139 v1.5 © Jennic 2008
4.3 OTP eFuse Memory
The JN5139 contains 48-bytes of eFuse memory; this is one time programmable memory that is organised as 12 x
32-bit words, 4 words are reserved by Jennic and 4 words are reserved for future use. The remaining 4 words are
fully user programmable, designed to allow for the storage of a 128-bit encryption key for secure external memory
encryption (see section 4.4.1)
For full details on how to program and use the eFuse memory, please refer to application note JN-AN-1062 Using
OTP eFuse Memory [3].
Alternatively, Jennic can provide an eFuse programming service for customers that wish to use the eFuse but do not
wish to undertake this for themselves. For further details of this service, please contact your local Jennic sales office.
4.4 External Memory
An external memory with an SPI interface may be used to provide storage for program code and data for the device
when external power is removed. The memory is connected to the SPI interface using select line SPISEL0; this
select line is dedicated to the external memory interface and is not available for use with other external devices. See
Figure 8 for connection details.
JN5139
Serial
Memory
SPISEL0
SPIMISO
SPIMOSI
SPICLK
SS
SDO
SDI
CLK
Figure 8: Connecting External Serial Memory
At reset, the contents of this memory are copied into RAM by the software boot loader. The Flash memory devices
that are supported as standard through the JN5139 bootloader are given in Table 1. Jennic recommends that where
possible one of these devices should be selected.
Manufacturer Device Number
ST Microelectronics M25P10-A
SST (Silicon Storage Technology) 25VF010
Table 1: Supported Flash Memories
Applications wishing to use an alternate Flash memory device should refer to application note JN-AN-1038
Programming Flash devices not supported by the JN51xx ROM-based bootloader [4]. This application note provides
guidance on developing an interface to an alternate device.
4.4.1 Secure External Memory Encryption
The contents of the external serial memory may be securely encrypted to protect against system cloning or intrusion.
The AES security processor combined with a user programmable 128-bit encryption key is used to encrypt the
contents of the external memory. The encryption key is stored in eFuse.
When bootloading program code from external serial memory, the JN5139 automatically accesses the encryption key
to execute the decryption process. User program code does not need to handle any of the decryption process; it is a
transparent process.