DS87C530/DS83C530 EPROM/ROM Microcontrollers with Real-Time Clock

DS87C530 SECURITY OPTIONS

The DS87C530 employs a standard three-level lock that restricts viewing of the EPROM contents. A 64- byte Encryption Array allows the authorized user to verify memory by presenting the data in encrypted form.

Lock Bits

The security lock consists of 3 lock bits. These bits select a total of 4 levels of security. Higher levels provide increasing security but also limit application flexibility. Table 10 shows the security settings. Note that the programmer cannot directly read the state of the security lock. User software has access to this information as described in the Memory section.

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 DS87C530 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 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 1.

DS87C530 Signature

The Signature bytes identify the product and programming revision to EPROM programmers. This information is at programming addresses 30h, 31h, and 60h. This information is as follows:

ADDRESS

VALUE

MEANING

 

 

 

30h

DAh

Manufacturer

31h

30h

Model

60h

01h

Extension

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