TSC87C51 TEMIC Semiconductors, TSC87C51 Datasheet - Page 10

• Manufacturer Part Number: TSC87C51
• Description: CMOS 0 to 25 MHz Programmable 8-bit Microcontroller
• Manufacturer: TEMIC Semiconductors

10
TSC87C51
EPROM
EPROM Structure
The TSC87C51 EPROM is divided in two different arrays:
D
D
In addition a third non programmable array is implemented:
D
EPROM Lock System
The program Lock system, when programmed, protects the on–chip program against software piracy.
Encryption Array
Within the EPROM array are 64 bytes of encryption array that are initially unprogrammed (all 1’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 encryption 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 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.
EPROM Programming
Set–up modes
In order to program and verify the EPROM or to read the signature bytes, the TSC87C51 is placed in specific set–up
modes (see Figure 6).
Control and program signals must be held at the levels indicated in Table 5.
Definition of terms
Address Lines:
Data Lines:
Control Signals:
Program Signals: ALE/PROG, EA/VPP.
Table 5 EPROM Set–up Modes
Program Code data
Verify Code data
Program Encryption Array
Address 0–3Fh
Read Signature Bytes
the code array:
the encryption array:
the signature array:
Mode
P1.0–P1.7, P2.0–P2.3 respectively for A0–A11
P0.0–P0.7 for D0–D7
RST, PSEN, P2.6, P2.7, P3.3, P3.6, P3.7.
RST
4 Kbytes.
64 bytes.
4 bytes.
1
1
1
1
PSEN
0
0
0
0
PROG
ALE/
1
1
EA/VPP
12.75V
12.75V
1
1
P2.6
0
0
0
0
P2.7
1
1
P3.3
1
0
1
0
Rev. E
P3.6
1
1
0
0
–
July 03, 2000
P3.7
1
1
1
0