參數(shù)資料
型號: 90S1200
廠商: Atmel Corp.
元件分類: 8位微控制器
英文描述: -bit AVR Microcontroller with 8K Bytes In- System Programmable Flash
中文描述: 位AVR微控制器具有8K字節(jié)的系統(tǒng)內(nèi)可編程閃存
文件頁數(shù): 25/71頁
文件大小: 1416K
代理商: 90S1200
25
AT90S1200
0838H
AVR
03/02
EEPROM Read/Write
Access
The EEPROM access registers are accessible in the I/O space.
The write access time is in the range of 2.5 - 4 ms, depending on the V
CC
voltages. A
self-timing function, however, lets the user software detect when the next byte can be
written. If the user code contains code that writes the EEPROM, some precaution must
be taken. In heavily filtered power supplies, V
CC
is likely to rise or fall slowly on Power-
up/down. This causes the device for some period of time to run at a voltage lower than
specified as minimum for the clock frequency used. CPU operation under these condi-
tions is likely cause the program counter to perform unintentional jumps and eventually
execute the EEPROM write code. To secure EEPROM integrity, the user is advised to
use an external under-voltage reset circuit in this case.
In order to prevent unintentional EEPROM writes, a specific write procedure must be fol-
lowed. Refer to
EEPROM Control Register
EECR
on page 25 for details on this.
When the EEPROM is read or written, the CPU is halted for two clock cycles before the
next instruction is executed.
EEPROM Address Register
EEAR
Bit 7, 6
Res: Reserved Bits
These bits are reserved bits in the AT90S1200 and will always read as zero.
Bits 5..0
EEAR5..0: EEPROM Address
The EEPROM Address Register (EEAR5..0) specifies the EEPROM address in the 64-
byte EEPROM space. The EEPROM data bytes are addressed linearly between 0 and
63.
EEPROM Data Register
EEDR
Bits 7..0
EEDR7..0: EEPROM Data
For the EEPROM write operation, the EEDR register contains the data to be written to
the EEPROM in the address given by the EEAR register. For the EEPROM read opera-
tion, the EEDR contains the data read out from the EEPROM at the address given by
EEAR.
EEPROM Control Register
EECR
Bits 7..2
Res: Reserved Bits
These bits are reserved bits in the AT90S1200 and will always be read as zero.
Bit
7
6
5
4
3
2
1
0
$1E
EEAR5
EEAR4
EEAR3
EEAR2
EEAR1
EEAR0
EEAR
Read/Write
R
R
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
$1D
MSB
LSB
EEDR
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
Bit
7
6
5
4
3
2
1
0
$1C
EEWE
EERE
EECR
Read/Write
R
R
R
R
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0
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