EZ80F91MCU ZILOG [Zilog, Inc.], EZ80F91MCU Datasheet - Page 129

• Manufacturer Part Number: EZ80F91MCU
• Description: eZ80Acclaim-TM Flash Microcontrollers
• Manufacturer: ZILOG [Zilog, Inc.]

PS019209-0504
Information Page Characteristics
Flash Control Registers
As noted earlier, the information page is not accessible using memory access
instructions and must be accessed via the I/O register. The Flash Page Select
Register contains a bit which selects the information page for I/O access.
There are two ways to erase the information page. The user can execute a MASS
ERASE operation, or the user can configure the Flash Page Select Register to
select the information page, and then execute a PAGE ERASE.
The Flash Control Register interface contains all of the registers used in Flash
memory. The definitions in this section describe each register.
Flash Key Register
Writing the two-byte sequence B6h, 49h in immediate succession to this register
unlocks the Flash Divider and Flash Write/Erase Protection registers. If these val-
ues are not written by consecutive CPU I/O Writes (I/O reads and memory Read/
Writes have no effect), the Flash Divider and Flash Write/Erase Protection regis-
ters remain locked. This prevents accidental overwrites of these critical Flash con-
trol register settings. Writing a value to either the Flash Frequency Divider register
or the Flash Write/Erase Protection register automatically relocks both of the reg-
isters. See Table 34.
Table 34. Flash Key Register
(FLASH_KEY = 00F5h)
Bit
Reset
CPU Access
Note: W = Write Only.
Bit
Position
[7:0]
FLASH_KEY
Value Description
B6h,
49h
Sequential Write operations of the values B6h, 49h to this
register will unlock the Flash Frequency Divider and Flash
Write/Erase Protection registers.
W
P R E L I M I N A R Y
7
0
W
6
0
W
5
0
W
4
0
W
3
0
Product Specification
W
2
0
eZ80F91 MCU
W
1
0
Flash Memory
W
0
0
110