Technical data

9.4.4
Accessing the Page Memory
Application Using the following operations, you can access pages organized in
bytes or words via an absolute memory address. The absolute
address is the total of the BR register contents and the constant
contained in the operation (-32768 to 32767).
Procedure of accessing
pages
The global area includes a "window" in the address area F400H to
FBFFH to allow access to one of maximum 256 memory areas
(= pages). A page occupies a maximum of 2 K addresses and can be
organized in bytes or words. Before each access to the page area, one
of the 256 pages must be selected by entering its page number in the
select register. Writing to the select register and the subsequent access
to the page area cannot be interrupted.
Before any access (load/transfer) to the page area, one of the 256
pages must be opened. To do this, you transfer the number of the page
to be opened to ACCU-1-L; this number is entered in the CPU
internal page register with the ACR operation. All subsequent page
operations write the contents of the page register to the select register
of the appropriate modules on the S5 bus before the page is accessed.
Changing the page register •• The page register is retained when the same program
processing level is
continued in another block called by the
jump operation (JU FB / JC FB).
•• When the page register is modified in a block, its value is
retained
if the program jumps back to the calling block at the end
of the block.
•• After another program processing level has been inserted, the
system program loads
the same value in the page register as it had
before the other level was inserted.
•• When the system program calls another program processing
level
, the page register is set to "0".
9
Operations with the Base Address Register (BR Register)
CPU 928B Programming Guide
C79000-B8576-C898-01
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