DS87C520 Datasheet, PDF (27/45 Pages) Dallas Semiconductor – EPROM/ROM High-Speed Micro

DS87C520/DS83C520 EPROM/ROM High-Speed Microcontrollers
Encryption Array
The Encryption Array allows an authorized user to verify EPROM without allowing the true memory 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 EPROM while the Encryption is unprogrammed (FFh). Once
the Encryption Array is programmed in a non-FFh state, the verify value will be encrypted.
For encryption to be effective, the Encryption Array must be unknown to the party that is trying to verify
memory. The entire EPROM also should be a non-FFh state or the Encryption Array can be discovered.
The Encryption Array is programmed as shown in Table 9. Note that the programmer cannot read the
array. Also note that the verify operation always uses the Encryption Array. The array has no impact
while FFh. Simply programming the array to a non-FFh state will cause the encryption to function.
OTHER EPROM OPTIONS
The DS87C520 has user selectable options that must be set before beginning software execution. These
options use EPROM bits rather than SFRs.
Program the EPROM selectable options as shown in Table 9. The Option Register sets or reads these
selections. The bits in the Option Control Register have the following function:
Bits 7 to 4 Reserved, program to a 1.
Bit 3
Watchdog POR default. Set = 1; watchdog reset function is disabled on power-up.
Set = 0; watchdog reset function is enabled automatically.
Bits 2 to 0 Reserved. Program to a 1.
SIGNATURE
The Signature bytes identify the product and programming revision to EPROM programmers. This
information is at programming addresses 30h, 31h, and 60h.
ADDRESS
30h
31h
60h
VALUE
DAh
20h
01h
MEANING
Manufacturer
Model
Extension
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