W78E516B
SECURITY
During the on-chip MTP-ROM programming mode, the MTP-ROM can be programmed and verified
repeatedly. Until the code inside the MTP-ROM is confirmed OK, the code can be protected. The
protection of MTP-ROM and those operations on it are described below.
The W78E516B has several Special Setting Registers, including the Security Register and
Company/Device ID Registers, which can not be accessed in programming mode. Those bits of the
Security Registers can not be changed once they have been programmed from high to low. They can
only be reset through erase-all operation. The contents of the Company ID and Device ID registers
have been set in factory. The Security Register is located at the 0FFFFH of the LDROM space.
D7 D6 D5 D4 D3 D2 D1 D0
0000h
0FFFh
Company ID (#DAH)
Device ID (#62H)
Security Bits
1
1
0
1
1
0
1
0
4KB MTP ROM
Program Memory
LDROM
0
1
1
0
0
0
1
0
64KB MTP ROM
Program Memory
APROM
B2 B1 B0
B7 Reserved
B0: Lock bit, logic 0: active
B1: MOVC inhibit,
Reserved
Reserved
logic 0: the MOVC instruction in external memory
cannot access the code in internal memory.
logic 1: no restriction.
B2: Encryption
logic 0: the encryption logic enable
logic 1: the encryption logic disable
FFFFh
Security Register
B07: Osillator Control
logic 0: 1/2 gain
logic 1: Full gain
Default 1 for all security bits.
Reserved bits must be kept in logic 1.
Special Setting Registers
Lock bit
This bit is used to protect the customer's program code in the W78E516B. It may be set after the
programmer finishes the programming and verifies sequence. Once this bit is set to logic 0, both the
MTP ROM data and Special Setting Registers can not be accessed again.
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.
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.
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