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CAT35C704JITE13 Datasheet(PDF) 4 Page - Catalyst Semiconductor |
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CAT35C704JITE13 Datasheet(HTML) 4 Page - Catalyst Semiconductor |
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4 / 14 page  4 Preliminary CAT35C704 Doc. No. 25045-00 2/98 PASSWORD PROTECTION The CAT35C704 is a 4K-bit E2PROM that features a password protection scheme to prevent unauthorized access to the information stored in the device. It contains an access code register which stores one to eight bytes of access code along with the length of that access code. Additionally, a memory pointer register stores the ad- dress that partitions the memory into protected and unprotected areas. As shipped from the factory, the device is unprogrammed and unprotected. The length of the access code is equal to zero and the memory pointer register points to location zero. Every byte of the device is fully accessible without an access code. Setting a password and moving the memory pointer register to cover all or part of the memory secures the device. Once secured, the memory is divided into a read/write area and a read-only area with the entry of a valid access code. If no access code is entered, the memory is divided into a read-only area and a non-access area. Figure 2 illlustrates this partitioning of the memory array. WRITE PROTECTION Another feature of the CAT35C704 is WRITE-protection without the use of an access code. If the memory pointer register is set to cover all or part of the memory, without setting the access code register, the device may be divided into an area which allows full access, and an area which allows READ-only access. To write into the READ-only area, the user can override the memory pointer register for every WRITE instruction or he can simply move the address in the memory pointer register to uncover this area, and then write into the memory. This mechanism prevents inadvertent overwriting of important data in the memory without the use of an access code. Figure 3 illustrates this partitioning of the memory array. 5074 FHD F03 Figure 2. Secure Mode 5074 FHD F04 ACCESS REGISTER: ACCESS CODE LENGTH: MEMORY POINTER: POINTER REGISTER ADDRESS IN MEMORY READ-ONLY ACCESS PASSWORD-ONLY ACCESS 255 (x16) 511 (x8) 0 ACCESS CODE (1–8 BYTES) 1 TO 8 a…a a…a Figure 1. A.C. Timing VCC CS CLK DI tVCCS DO tCSS tCKH tCKL tCSH tHZ tDIH tDIS tPD tPD HIGH-Z HIGH-Z |
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