Datasheet

2487D–MICRO–6/08

AT89S51

Dual Data Pointer Registers: To facilitate accessing both internal and external data memory,

two banks of 16-bit Data Pointer Registers are provided: DP0 at SFR address locations 82H-

83H and DP1 at 84H-85H. Bit DPS = 0 in SFR AUXR1 selects DP0 and DPS = 1 selects DP1.

The user should ALWAYS initialize 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 rest under software control and is not affected by

reset.

Table 5-2. AUXR: Auxiliary Register

AUXR Address = 8EH Reset Value = XXX00XX0B

Not Bit Addressable

– – – WDIDLE DISRTO – – DISALE

Bit

765 4 3 2 1 0

– Reserved for future expansion

DISALE Disable/Enable ALE

DISALE

Operating Mode

0 ALE is emitted at a constant rate of 1/6 the oscillator frequency

1 ALE is active only during a MOVX or MOVC instruction

DISRTO Disable/Enable Reset-out

DISRTO

0 Reset pin is driven High after WDT times out

1 Reset pin is input only

WDIDLE Disable/Enable WDT in IDLE mode

WDIDLE

0 WDT continues to count in IDLE mode

1 WDT halts counting in IDLE mode