DS87C520 datasheet(28/45 Pages) DALLAS

28 / 45 page

DS87C520/DS83C520 EPROM/ROM High-Speed Microcontrollers

28 of 45

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.

DS87C520 Datasheet(PDF) 28 Page - Dallas Semiconductor