Maxim DS87C530 Clock User Manual

Open as PDF

of 47

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

29 of 47

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

WWW.100Y.COM.TW WWW.100Y.COM.TW WWW.100Y.COM.TW

previous next

Top Automotive Device Types

Top Automotive Brands

Top Baby Care Device Types

Top Baby Care Brands

Top Car Audio & Video Device Types

Top Car Audio & Video Brands

Top Cellphone Device Types

Top Cellphone Brands

Top Communications Device Types

Top Communications Brands

Top Computer Device Types

Top Computer Brands

Top Fitness Device Types

Top Fitness Brands

Top Home Audio Device Types

Top Home Audio Brands

Top Household Appliance Device Types

Top Household Appliance Brands

Top Kitchen Appliance Device Types

Top Kitchen Appliance Brands

Top Laundry Appliance Device Types

Top Laundry Appliance Brands

Top Lawn & Garden Device Types

Top Lawn & Garden Brands

Top Marine Equipment Device Types

Top Marine Equipment Brands

Top Musical Instrument Device Types

Top Musical Instrument Brands

Top Outdoor Cooking Device Types

Top Outdoor Cooking Brands

Top Personal Care Device Types

Top Personal Care Brands

Top Photography Device Types

Top Photography Brands

Top Portable Media Device Types

Top Portable Media Brands

Top Power Tools Device Types

Top Power Tools Brands

Top TV and Video Device Types

Top TV and Video Brands

Top Videogame Device Types

Top Videogame Brands

Maxim DS87C530 Clock User Manual