6.16 OB 180: Variable Data Block Access
Using OB 180
You can use OB 180 when working with data blocks that are longer
than 261 words (incl. 5 words header).
Using OB 180, you can shift an "access window" of 256 data words in
steps of 16 words over a data block (at paragraph addresses). Call
OB 180 each time you want to shift the access window further.
In contrast to the CPU 928B, you cannot shift the access window
continuously but only in steps that are multiples of 16.
Function
When you use OB 180, the start address of the current data block is
shifted towards the end of the block by the specified value. This takes
into account that the length of DB still available is reduced (DBA and
DBL registers are loaded in keeping with the shift, see Sections 8.3
and 9.2.1).
Note
Before calling OB 180, a data block (DB or DX) with an adequate
length must already be open.
Parameters
ACCU-1-L
Shift number S: Number of data words, by which the data block start
address will be shifted.
Permitted values: 0 ≤ V < DBL, S = n * 16 (16, 32, 48 ...)
Result
After you have called OB 180 succesfully:
•• the relative address of DW 0 is shifted by the value contained in
ACCU-1-L (the DBA and DBL registers are updated accordingly),
•• the RLO is cleared (RLO = 0),
•• all other bit and word codes are cleared,
•• the content of ACCU-1-L = 0.
OB 180: Variable Data Block Access
CPU 948 Programming Guide
C79000-G8576-C848-04
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