DS83C520_07 Datasheet, PDF (28/43 Pages) Dallas Semiconductor – EPROM/ROM High-Speed Microcontrollers

DS87C520/DS83C520 EPROM/ROM High-Speed Microcontrollers
Figure 5. EPROM Programming Configuration
ROM-SPECIFIC FEATURES
The DS83C520 supports a subset of the EPROM features found on the DS87C520.
SECURITY OPTIONS
Lock Bits
The DS83C520 employs a lock that restricts viewing of the ROM contents. When set, the lock will
prevent MOVC instructions in external memory from reading program bytes in internal memory. When
locked, the EA pin is sampled and latched on reset. The lock setting is enabled or disabled when the
devices are manufactured according to customer specifications. The lock bit cannot be read in software,
and its status can only be determined by observing the operation of the device.
Encryption Array
The DS83C520 Encryption Array allows an authorized user to verify ROM without allowing the true
memory contents to be dumped. During a verify, each byte is Exclusive NORed (XNOR) with a byte in
the Encryption Array. This results in a true representation of the ROM while the Encryption is
unprogrammed (FFh). Once the Encryption Array is programmed in a non-FFh state, the Encryption
Array is programmed (or optionally left unprogrammed) when the devices are manufactured according to
customer specifications.
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