Philips Semiconductors
Preliminary specification
80C51 8-bit microcontroller
8K/256 OTP, 8 channel 10 bit A/D, I2C, PWM,
capture/compare, high I/O, low voltage (2.7V–5.5V), low power
P87C552
EPROM CHARACTERISTICS
Security Bits
The 87C552 contains three signature bytes that can be read and
used by an EPROM programming system to identify the device. The
signature bytes identify the device as an 87C552 manufactured by
Philips:
With none of the security bits programmed the code in the program
memory can be verified. If the encryption table is programmed, the
code will be encrypted when verified. When only security bit 1 (see
Table 11) is programmed, MOVC instructions executed from external
program memory are disabled from fetching code bytes from the
internal memory, EA is latched on Reset and all further programming
of the EPROM is disabled. When security bits 1 and 2 are
(030H) = 15H indicates manufactured by Philips Components
(031H) = 93H indicates 87C552
(60H) = 01H
programmed, in addition to the above, verify mode is disabled.
Program Verification
If security bits 2 or 3 have not been programmed, the on-chip
program memory can be read out for program verification.
When all three security bits are programmed, all of the conditions
above apply and all external program memory execution is disabled.
If the encryption table has been programmed, the data presented at
port 0 will be the exclusive NOR of the program byte with one of the
encryption bytes. The user will have to know the encryption table
contents in order to correctly decode the verification data. The
encryption table itself cannot be read out.
Table 11. Program Security Bits for EPROM Devices
1, 2
PROGRAM LOCK BITS
SB1
SB2
SB3 PROTECTION DESCRIPTION
1
2
3
U
U
U
No Program Security features enabled. (Code verify will still be encrypted by the Encryption Array if
programmed.)
P
U
U
MOVC instructions executed from external program memory are disabled from fetching code bytes from
internal memory, EA is sampled and latched on Reset, and further programming of the EPROM is disabled.
P
P
P
P
U
P
Same as 2, also verify is disabled.
4
Same as 3, external execution is disabled.
NOTES:
1. P – programmed. U – unprogrammed.
2. Any other combination of the security bits is not defined.
2
2
Purchase of Philips I C components conveys a license under the Philips’ I C patent
2
to use the components in the I C system provided the system conforms to the
I C specifications defined by Philips. This specification can be ordered using the
2
code 9398 393 40011.
72
1999 Mar 30
NXP [ NXP ]
