AT89S53
Dual Data Pointer Registers To facilitate accessing exter-
nal data memory, two banks of 16 bit Data Pointer Regis-
ters are provided: DP0 at SFR address locations 82H-83H
and DP1 at 84H-85H. Bit DPS = 0 in SFR WCON selects
DP0 and DPS = 1 selects DP1. The user should always ini-
talize the DPS bit to the appropriate value before accessing
the respective Data Pointer register.
Power Off Flag The Power Off Flag (POF) is located at
bit_4 (PCON.4) in the PCON SFR. POF is set to “1” during
power up. It can be set and reset under software control
and is not affected by RESET.
Table 3. WCON—Watchdog Control Register
WCON Address = 96H
Reset Value = 0000 0010B
PS2
7
PS1
6
PS0
5
reserved
4
reserved
3
DPS
2
WDTRST
1
WDTEN
0
Bit
Symbol
Function
PS2
PS1
PS0
Prescaler Bits for the Watchdog Timer. When all three bits are set to “0”, the watchdog timer has a nominal period of 16
ms. When all three bits are set to “1”, the nominal period is 2048 ms.
DPS
Data Pointer Register Select. DPS = 0 selects the first bank of Data Pointer Register, DP0, and DPS = 1 selects the
second bank, DP1
WDTRST
WDTEN
Watchdog Timer Reset. Each time this bit is set to “1” by user software, a pulse is generated to reset the watchdog timer.
The WDTRST bit is then automatically reset to “0” in the next instruction cycle. The WDTRST bit is Write-Only.
Watchdog Timer Enable Bit. WDTEN = 1 enables the watchdog timer and WDTEN = 0 disables the watchdog timer.
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ATMEL [ ATMEL ]
