C508_01 Datasheet, PDF (49/267 Pages) Infineon Technologies AG – 8-Bit CMOS Microcontroller

C508
Special Function Register DPSEL (Address 92_H)
Bit No. MSB
7
6
5
4
3
2
92_H
–
–
–
–
–
.2
External Bus Interface
Reset Value: XXXXX000_B
LSB
1
0
.1
.0 ^DPSEL
Bit
DPSEL.2-0
Function
Data Pointer Select bits
DPSEL.2-0 defines the number of the actual active data pointer,
DPTR0-7.
- - - - - .2 .1 .0
DPSEL(92 _H)
DPSEL
Selected
Data-
.2 .1 .0 pointer
0 0 0 DPTR 0
0 0 1 DPTR 1
0 1 0 DPTR 2
0 1 1 DPTR 3
1 0 0 DPTR 4
1 0 1 DPTR 5
1 1 0 DPTR 6
1 1 1 DPTR 7
DPTR7
DPH(83H) DPL(82H)
DPTR0
External Data Memory
MCD00779
Figure 4-3 Accessing of External Data Memory via Multiple Datapointers
4.6.3 Advantages of Multiple Datapointers
This mechanism for addressing external data memory results in less code and faster
execution of external accesses. Whenever the contents of the datapointer must be
altered between two or more 16-bit addresses, one single instruction to select a new
datapointer is sufficient. lf the program uses only one datapointer, then it must save the
old value (with two 8-bit instructions) and load the new address, byte-by-byte. This not
only takes more time, it also requires additional space in the internal RAM.
User’s Manual
4-7
2001-05