W78IRD2 Datasheet, PDF (59/76 Pages) Winbond – 8-BIT MICROCONTROLLER

W78IRD2
17. OPTION BITS REGISTER
In the on-chip Flash EPROM writer programming mode mode, the flash EPROM can be programmed
and verified repeatedly. Until the code is ready, it can be protected by properly setting option bits.
Option bits control the initial configuration of W78IRD2, including code protection, system clock mode
selection (6T/12T), H/W reboot mode selection and oscillator control.
D7 D6 D5 D4 D3 D2 D1 D0
B7 B6 B5 B4 B3 B2 B1 B0
B0: Lock bit, Logic 0 is active
Option Bits
B1: MOVC Inhibit, Logic 0 is active
B2: Encryption bit, Logic 0 is active
B3: logic 1 is 12 clock per machine cycle
logic 0 is 6 clock per machine cycle
B4: Enable P2.7 and P2.6 as H/W Reboot Function
logic 1: P2.7 and P2.6 are as I/O Function
logic 0: P2.7 and P2.6 are as H/W Reboot Function
B5: Enable P4.3 as H/W Reboot Function
logic 1: P4.3 is as I/O Function
logic 0: P4.3 is as H/W Reboot Function
B6: Reserved (0)
B7: Logic 1: The Crystal Frequency is above 25MHz
Logic 0: The Crystal Frequency is under 25MHz
4KB Flash EPROM
Program Memory
LD Flash EPROM
0000H
0FFFH
Reserved
64KB Flash EPROM
Program Memory
AP Flash EPROM
Option Bits Register FFFFH
Default 1 is for all Security Bits.
The Reserved bit must be kept in logic 1.
Option Bits Register
Lock bit
This bit is used to protect the code in the W78IRD2. It may be set after the programmer finishes
programming and verifies the sequence. Once this bit is set to logic-0, both the Flash EPROM data and
Option Bits Register cannot be accessed again.
MOVC Inhibit
This bit is used to restrict the accessible region of the MOVC instruction. It can prevent a 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 can only access code in external
memory, not in internal memory. A MOVC instruction in internal program memory can always access
both internal and external memory. If this bit is logic-1, there are no restrictions on MOVC.
Encryption
This bit is used to enable and disable the encryption logic for code protection. Once encryption is
enabled, the data presented on port 0 is encoded via encryption logic. This bit can be reset only by
erasing the whole chip.
Oscillator Control
The gain of the on-chip oscillator amplifier can be reduced by bit B7 in the option bits register. If bit 7 is
set to zero, the gain is cut in half.
According the circuit in Figure 20-1, the values of R, C1 and C2 may need some adjustment when
running at lower gain. Furthermore, reducing the gain by one-half may improperly affect an external
crystal running at frequencies above 20 MHz.
- 59 -
Publication Release Date: October 2, 2006
Revision A7