Dual Data Pointer Register - Atmel AT89C5131A-L Manual

Dual Data Pointer
Register
Figure 12. Use of Dual Pointer
7
AUXR1(A2H)
4338F–USB–08/07
The additional data pointer can be used to speed up code execution and reduce code
size.
The dual DPTR structure is a way by which the chip will specify the address of an exter-
nal data memory location. There are two 16-bit DPTR registers that address the external
memory, and a single bit called DPS = AUXR1.0 (see Table 32) that allows the program
code to switch between them (see Figure 12).
0
DPS
DPTR1
DPH(83H) DPL(82H)
Table 32. AUXR1 Register
AUXR1- Auxiliary Register 1(0A2h)
7 6
- -
Bit Bit
Number Mnemonic
7 -
6 -
5 ENBOOT
4 -
3 GF3
2 0
1 -
0 DPS
Reset Value = XX[BLJB]X X0X0b
Not bit addressable
a. Bit 2 stuck at 0; this allows to use INC AUXR1 to toggle DPS without changing GF3.
DPTR0
5 4
ENBOOT -
Description
Reserved
The value read from this bit is indeterminate. Do not set this bit.
Reserved
The value read from this bit is indeterminate. Do not set this bit.
Enable Boot Flash
Cleared to disable boot ROM.
Set to map the boot ROM between F800h - 0FFFFh.
Reserved
The value read from this bit is indeterminate. Do not set this bit.
This bit is a general-purpose user flag.
Always cleared.
Reserved
The value read from this bit is indeterminate. Do not set this bit.
Data Pointer Selection
Cleared to select DPTR0.
Set to select DPTR1.
AT89C5131A-L
External Data Memory
3 2 1
GF3 0 -
0
DPS
25