87C752 Philips Semiconductors, 87C752 Datasheet - Page 17

• Manufacturer Part Number: 87C752
• Description: 80C51 8-bit microcontroller family 2K/64 OTP/ROM/ 5 channel 8 bit A/D/ I2C/ PWM/ low pin count
• Manufacturer: Philips Semiconductors

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Philips Semiconductors
A high voltage V
(This sets Port 1 as an input port). The data to be programmed into
the EPROM array is then placed on Port 1. This is followed by a
series of programming pulses applied to the PGM/ pin (P0.1). These
pulses are created by driving P0.1 low and then high. This pulse is
repeated until a total of 25 programming pulses have occurred. At
the conclusion of the last pulse, the PGM/ signal should remain high.
The V
87C752 in the verify mode. (Port 1 is now used as an output port).
After four machine cycles (48 clock periods), the contents of the
addressed location in the EPROM array will appear on Port 1.
The next programming cycle may now be initiated by placing the
address information at the inputs of the multiplexed buffers, driving
the V
programmed to Port1 and issuing the 26 programming pulses on the
PGM/ pin, bringing V
byte.
Programming Modes
The 87C752 has four programming features incorporated within its
EPROM array. These include the USER EPROM for storage of the
application’s code, a 16-byte encryption key array and two security
bits. Programming and verification of these four elements are
selected by a combination of the serial data stream applied to the
RESET pin and the voltage levels applied to port pins P0.1 and
P0.2. The various combinations are shown in Table 4.
Encryption Key Table
The 87C752 includes a 16-byte EPROM array that is programmable
by the end user. The contents of this array can then be used to
encrypt the program memory contents during a program memory
verify operation. When a program memory verify operation is
performed, the contents of the program memory location is
XNOR’ed with one of the bytes in the 16-byte encryption table. The
resulting data pattern is then provided to port 1 as the verify data.
The encryption mechanism can be disable, in essence, by leaving
the bytes in the encryption table in their erased state (FFH) since
the XNOR product of a bit with a logical one will result in the original
bit. The encryption bytes are mapped with the code memory in
16-byte groups. the first byte in code memory will be encrypted with
the first byte in the encryption table; the second byte in code
Table 4. Implementing Program/Verify Modes
NOTE:
1999 Jul 23
Program user EPROM
Verify user EPROM
Program key EPROM
Verify key EPROM
Program security bit 1
Program security bit 2
Verify security bits
80C51 8-bit microcontroller family
2K/64 OTP/ROM, 5 channel 8 bit A/D, I
Pulsed from V
PP
PP
pin to the V
signal may now be driven to the V
PP
IH
level is then applied to the V
PP
to V
PP
voltage level, providing the byte to be
OPERATION
back down to the V
IL
and returned to V
OH
C
IH
level and verifying the
.
level, placing the
PP
input (P0.2).
2
C, PWM, low pin count
SERIAL CODE
17
296H
296H
292H
292H
29AH
298H
29AH
memory will be encrypted with the second byte in the encryption
table and so forth up to and including the 16the byte. The encryption
repeats in 16-byte groups; the 17th byte in the code memory will be
encrypted with the first byte in the encryption table, and so forth.
Security Bits
Two security bits, security bit 1 and security bit 2, are provided to
limit access to the USER EPROM and encryption key arrays.
Security bit 1 is the program inhibit bit, and once programmed
performs the following functions:
1. Additional programming of the USER EPROM is inhibited.
2. Additional programming of the encryption key is inhibited.
3. Verification of the encryption key is inhibited.
4. Verification of the USER EPROM and the security bit levels may
(If the encryption key array is being used, this security bit should be
programmed by the user to prevent unauthorized parties from
reprogramming the encryption key to all logical zero bits. Such
programming would provide data during a verify cycle that is the
logical complement of the USER EPROM contents).
Security bit 2, the verify inhibit bit, prevents verification of both the
USER EPROM array and the encryption key arrays. The security bit
levels may still be verified.
Programming and Verifying Security Bits
Security bits are programmed employing the same techniques used
to program the USER EPROM and KEY arrays using serial data
streams and logic levels on port pins indicated in Table 4. When
programming either security bit, it is not necessary to provide
address or data information to the 87C752 on ports 1 and 3.
Verification occurs in a similar manner using the RESET serial
stream shown in Table 4. Port 3 is not required to be driven and the
results of the verify operation will appear on ports 1.6 and 1.7.
Ports 1.7 contains the security bit 1 data and is a logical one if
programmed and a logical zero if not programmed. Likewise, P1.6
contains the security bit 2 data and is a logical one if programmed
and a logical zero if not programmed.
still be performed.
P0.1 (PGM/)
V
V
V
–*
–*
–*
–*
IH
IH
IH
83C752/87C752
Product specification
P0.2 (V
V
V
V
V
V
V
V
PP
PP
PP
PP
IH
IH
IH
PP
)