Technical data

Continuation of the example:
Because the DBL register is adjusted at the same time,
error monitoring
is guaranteed
: the operation T DW 5 is permitted, while T DW 6/LW 6
would cause an error.
If you call OB 180 again, the DBA can be increased again (and the DBL is
further reduced). The operation C DB 17 re-establishes the initial state
(DBA = 151B, DBL = 8).
If DB 17 has a length of, for example, 258 data words, you cannot access
DW 256 and DW 257 using STEP 5 operations. If you shift the DBA register
by two, you can address data words 256 and 257 using "DW 254" and
"DW 255".
For more information about the DBA/DBL registers, refer to Chapter 9.
eeee
f f f f
gggg
cccc
dddd
hhhh
1516
1517
151B
151C
151D
151E
151F
1520
1521
1522
DW 0
DW 1
DW 2
DW 3
DW 4
DW 5
Addr. (hex.) DB 17
DBA
new
.
.
.
.
5 words
block header
DBL
old
DBL
new
DBA
old
15 0
Fig. 6-6 Shifting the DB start address
6
OB 180: Accessing Variable Data Blocks
CPU 928B Programming Guide
C79000-B8576-C898-01
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