TS87C54X2 Temic Semiconductors, TS87C54X2 Datasheet - Page 35

• Manufacturer Part Number: TS87C54X2
• Description: 8-bit CMOS Microcontroller 0-60 MHz
• Manufacturer: Temic Semiconductors

7. TS80C54/58X2 ROM
7.1 ROM Structure
The TS80C54/58X2 ROM memory is in three different arrays:
7.2 ROM Lock System
The program Lock system, when programmed, protects the on-chip program against software piracy.
7.2.1 Encryption Array
Within the ROM array are 64 bytes of encryption array that are initially unprogrammed (all FF’s). Every time a
byte is addressed during program verify, 6 address lines are used to select a byte of the encryption array. This
byte is then exclusive-NOR’ed (XNOR) with the code byte, creating an encrypted verify byte. The algorithm, with
the encryption array in the unprogrammed state, will return the code in its original, unmodified form.
When using the encryption array, one important factor needs to be considered. If a byte has the value FFh, verifying
the byte will produce the encryption byte value. If a large block (>64 bytes) of code is left unprogrammed, a
verification routine will display the content of the encryption array. For this reason all the unused code bytes
should be programmed with random values. This will ensure program protection.
7.2.2 Program Lock Bits
The lock bits when programmed according to Table 20. will provide different level of protection for the on-chip
code and data.
U: unprogrammed
P: programmed
7.2.3 Signature bytes
The TS80C54/58X2 contains 4 factory programmed signatures bytes. To read these bytes, perform the process
described in section 8.3.
7.2.4 Verify Algorithm
Refer to 8.3.4
Rev. B - Aug. 31, 1999
Securi-
ty level
the code array: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16/32 Kbytes.
the encryption array: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 bytes.
the signature array:. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 bytes.
1
2
Program Lock Bits
LB1
U
P
LB2
U
U
LB3
U
U
Table 20. Program Lock bits
No program lock features enabled. Code verify will still be encrypted by the encryption
array if programmed. MOVC instruction executed from external program memory returns
non encrypted data.
MOVC instruction executed from external program memory are disabled from fetching
code bytes from internal memory, EA is sampled and latched on reset.
Protection description
TS80C54X2/C58X2
TS87C54X2/C58X2
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