80C51 Datasheet, PDF (19/38 Pages) NXP Semiconductors – 80C51 8-bit microcontroller family 4K/128 OTP/ROM/ROMless low voltage 2.7V.5.5V, low power, high speed 33 MHz

Philips Semiconductors
80C51 8-bit microcontroller family
4K/128 OTP/ROM/ROMless, low voltage (2.7V–5.5V),
low power, high speed (33 MHz)
Product specification
80C51/87C51/80C31
Reduced EMI Mode
The AO bit (AUXR.0) in the AUXR register when set disables the
ALE output.
Reduced EMI Mode
AUXR (8EH)
7
6
5
4
3
2
1
0
–
–
–
–
–
–
–
AO
AUXR.0
AO
Turns off ALE output.
Dual DPTR
The dual DPTR structure (see Figure 13) enables a way to specify
the address of an external data memory location. There are two
16-bit DPTR registers that address the external memory, and a
single bit called DPS = AUXR1/bit0 that allows the program code to
switch between them.
• New Register Name: AUXR1#
• SFR Address: A2H
• Reset Value: xxx000x0B
AUXR1 (A2H)
7
6
5
4
3
2
1
0
–
–
–
LPEP WUPD
0
–
DPS
Where:
DPS = AUXR1/bit0 = Switches between DPTR0 and DPTR1.
Select Reg
DPTR0
DPTR1
DPS
0
1
The DPS bit status should be saved by software when switching
between DPTR0 and DPTR1.
Note that bit 2 is not writable and is always read as a zero. This
allows the DPS bit to be quickly toggled simply by executing an INC
DPTR insstruction without affecting the WOPD or LPEP bits.
DPS
BIT0
AUXR1
DPH
(83H)
DPL
(82H)
DPTR1
DPTR0
Figure 13.
EXTERNAL
DATA
MEMORY
SU00745A
DPTR Instructions
The instructions that refer to DPTR refer to the data pointer that is
currently selected using the AUXR1/bit 0 register. The six
instructions that use the DPTR are as follows:
INC DPTR
MOV DPTR, #data16
MOV A, @ A+DPTR
MOVX A, @ DPTR
MOVX @ DPTR , A
JMP @ A + DPTR
Increments the data pointer by 1
Loads the DPTR with a 16-bit constant
Move code byte relative to DPTR to ACC
Move external RAM (16-bit address) to
ACC
Move ACC to external RAM (16-bit
address)
Jump indirect relative to DPTR
The data pointer can be accessed on a byte-by-byte basis by
specifying the low or high byte in an instruction which accesses the
SFRs. See application note AN458 for more details.
2000 Jan 20
19