EZ80F91MCU Datasheet, PDF (129/396 Pages) Zilog, Inc. – eZ80Acclaim-TM Flash Microcontrollers

eZ80F91 MCU
Product Specification
110
Information Page Characteristics
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.
Flash Control Registers
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.
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
W
W
W
W
W
W
W
W
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.
PS019209-0504
PRELIMINARY
Flash Memory