W78E516B_06 Datasheet, PDF (20/37 Pages) Winbond – 8-BIT MICROCONTROLLER

W78E516B
6. SECURITY
During the on-chip Flash EPROM programming mode, the Flash EPROM can be programmed and
verified repeatedly. Until the code inside the Flash EPROM is confirmed OK, the code can be
protected. The protection of Flash EPROM and those operations on it are described below.
The W78E516B has a Special Setting Register, the Security Register, which can not be accessed in
programming 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 located at the 0FFFFH of the LDROM space.
D7 D6 D5 D4 D3 D2 D1 D0
B7 Reserved B2 B1 B0
Security Bits
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.
B2: Encryption
logic 0: the encryption logic enable
logic 1: the encryption logic disable
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.
0000h
4KB Flash EPROM
Program Memory
LDROM
0FFFh
64KB Flash EPROM
RReeseerrvveedd
Program Memory
APROM
Security Register ^FFFFh
Special Setting Register
6.1 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
Flash EPROM data and Special Setting Registers 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.
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