W78E52C/W78E052C

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6. SECURITY BITS

During the on-chip Flash EPROM operation mode, the ROM can be programmed and verified

repeatedly. Until the code inside the ROM is confirmed OK, the code can be protected. The protection

of ROM and those operations on it are described below.

The W78E052C has a Security Register which can not be accessed in normal mode. These registers

can only be accessed from the Flash EPROM operation mode. Those bits of the Security Register can

not be changed once they have been programmed from high to low. They can only be reset through

erase-all operation. The Security Register is addressed in the Flash EPROM operation mode by

address #0FFFFh.

B0

B1

B0 : Lock bit, logic 0 : active

B1 : MOVC inhibit,

logic 0 : the MOVC instruction in external memory

cannot access the code in internal memory.

logic 1 : no restriction.

Default 1 for all security bits.

Special Setting Register

Security Bits

8KB On-chip ROM

Program Memory

Reserved

Security Register

0FFFFh

0000h

1FFFh

Reserved

B2

B2 : Encryption

logic 0 : the encryption logic enable

logic 1 : the encryption logic disable

Reserved bits must be kept in logic 1.

B7

B7 : Osillator Control

logic 0 : 1/2 gain

logic 1 : Full gain

6.1 Lock Bit

This bit is used to protect the customer's program code in the W78E052C. It may be set after the

programmer finishes the programming and verifies sequence. Once this bit is set to logic 0, both the

ROM data and Special Setting Register can not be accessed again.

6.2 MOVC Inhibit

This bit is used to restrict the accessible region of the MOVC instruction. It can prevent the MOVC

instruction in external program memory from reading the internal program code. When this bit is set to

logic 0, a MOVC instruction in external program memory space will be able to access code only in the

external memory, not in the internal memory. A MOVC instruction in internal program memory space

will always be able to access the ROM data in both internal and external memory. If this bit is logic 1,

there are no restrictions on the MOVC instruction.

6.3 Encryption

This bit is used to enable/disable the encryption logic for code protection. Once encryption feature is

enabled, the data presented on port 0 will be encoded via encryption logic. Only whole chip erase will

reset this bit.