2001 Apr 06

17

Philips Semiconductors

Preliminary specification

P87C51MB2/P87C51MC2

80C51 8-bit microcontroller family with extended memory

64KB/96KB OTP with 2KB/3KB RAM

SECURITY BITS

The P87C51Mx2 has security bits to protect users’ firmware codes. With none of the security bits programmed, the code in the

program memory can be verified. With only security bit 1 (see Table 6) 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 EPROM is disabled. When security bits 1 and 2 are programmed, in addition to the above, verify mode is

disabled. When all three security bits are programmed, all of the conditions above apply and all external program memory

execution is disabled.

Protection Description

Bit 1

Bit 2

Bit 3

1

U

U

U

No program security features enabled. EEPROM is programmable and verifiable.

2

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.

3

P

P

U

Same as 2, also verification is disabled.

4

P

P

P

Same as 3, external execution is disabled.

Notes:

1. P - programmed. U- unprogrammed.

2. Any other combination of security bits is not defined.

Table 6: EPROM Security Bits