Technical data

You specify the page to be used when you assign parameters to the
special function organization blocks OB 216, OB 217 and OB 218.
The number of the "currently active" page is then automatically
entered in a memory location with the address 0FEFFH (see Fig.
6-11). All addresses then refer to the page whose number is entered.
Note
You cannot read the page address register with the address
0FEFF H. At this address, you can, however, read out the bus
error register on the coordinator module 923C (see
S5-135U/155U System Manual).
Notes on assigning
parameters
When a byte/word/double word is written (OB 216) and read
(OB 217) to/from a page, the bytes are referenced in the following
order:
Byte
High byte
Low byte
7
Byte format
Word format
Double word format
Address n
Address n
Address n+1
Address n
Address n+1
Address n+2
Address n+3
0
H byte in H word
L byte in H word
H byte in L word
L byte in L word
Fig. 6-12 Location of the bytes when writing (OB 216) / reading (OB 217) to/from a page in words or double
words
6
OB 216 to OB 218: Page Access
CPU 928B Programming Guide
C79000-B8576-C898-01
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