C509-L_97 SIEMENS [Siemens Semiconductor Group], C509-L_97 Datasheet - Page 59

• Manufacturer Part Number: C509-L_97
• Description: 8-Bit CMOS Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

Figure 4-3
Accessing of External Data Memory via Multiple Datapointers
4.3.3 Advantages of Multiple Datapointers
Using the above addressing mechanism for 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, which selects a new datapointer, does this job.
lf the program uses just one datapointer, then it has to 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.
4.3.4 Application Example and Performance Analysis
The following example shall demonstrate the involvement of multiple data pointers in a table
transfer from the code memory to external data memory.
Start address of ROM source table:
Start address of table in external RAM:
Semiconductor Group
DPSEL(92 )
DPSEL
-
.2
0
0
0
0
1
1
1
1
-
.1
0
0
1
1
0
0
1
1
-
H
-
.0
0
1
0
1
0
1
0
1
-
Selected
Data-
pointer
DPTR 0
DPTR 1
DPTR 2
DPTR 3
DPTR 4
DPTR 5
DPTR 6
DPTR 7
.2
.1
.0
DPH(83 )
H
4-7
1FFF H
2FA0 H
DPL(82 )
H
DPTR7
DPTR0
External Bus Interface
External Data Memory
1997-10-01
MCD00779
C509-L