XC864 Datasheet, PDF (23/118 Pages) Infineon Technologies AG – 8-Bit Single-Chip Microcontroller

XC864
Functional Description
In order to access a register located in a page different from the actual one, the current
page must be left. This is done by reprogramming the bit field PAGE in the page register.
Only then can the desired access be performed.
If an interrupt routine is initiated between the page register access and the module
register access, and the interrupt needs to access a register located in another page, the
current page setting can be saved, the new one programmed and finally, the old page
setting restored. This is possible with the storage fields STx (x = 0 - 3) for the save and
restore action of the current page setting. By indicating which storage bit field should be
used in parallel with the new page value, a single write operation can:
• Save the contents of PAGE in STx before overwriting with the new value
(this is done in the beginning of the interrupt routine to save the current page setting
and program the new page number); or
• Overwrite the contents of PAGE with the contents of STx, ignoring the value written to
the bit positions of PAGE
(this is done at the end of the interrupt routine to restore the previous page setting
before the interrupt occurred)
STNR
value update
from CPU
ST3
ST2
ST1
ST0
PAGE
Figure 9 Storage Elements for Paging
With this mechanism, a certain number of interrupt routines (or other routines) can
perform page changes without reading and storing the previously used page information.
The use of only write operations makes the system simpler and faster. Consequently,
this mechanism significantly improves the performance of short interrupt routines.
The XC864 supports local address extension for:
• Parallel Ports
• Analog-to-Digital Converter (ADC)
• Capture/Compare Unit 6 (CCU6)
• System Control Registers
The page register has the following definition:
Data Sheet
19
V 1.1, 2009-03