Technical data

6.31 OB 240 to 242: Special Functions for Shift Registers
6.31.1
Shift Registers
This introduction tells you what you can use shift registers for and the
points to note in doing so.
Application You can use shift registers, e.g. in a manufacturing process, to
program a materials follow-up on the programmable controller. On
the CPU 928B, you have a maximum of 64 software shift registers
available.
You can write data to the shift register and read data from it. This is
done using "pointers". Pointers are flag bytes that contain the contents
of individual cells of a shift register.
Structure A software shift register consists of rows of 8-bit wide memory cells
and can be between 2 and 256 memory cells long.
Location in the DB-RAM The data of a shift register are located in the data block RAM of the
CPU. Each shift register is assigned to a specific data block and also
has the same number as the data block (permitted: 192 to 255). If you
set up a shift register with the number 210, the corresponding data is
in data block DB 210.
The DB-RAM has a capacity of 46 Kbytes (address KH 8000 to KH
DD7F). This area contains the data blocks (starting from KH 8000 in
ascending order) copied using OB 254 and 255 and the shift registers
you have set up (starting from KH DD7F in descending order). If the
memory area of the DB RAM is not sufficient for copying DBs or
setting up shift registers, the CPU recognizes a runtime error and calls
OB 31. The reactions to the error depend on how you have
programmed OB 31 (see Section 5.6.2).
The following schematics illustrate the principle of a software shift
register with three pointers and twelve memory cells.
6
OB 240 to 242: Special Functions for Shift Registers
CPU 928B Programming Guide
C79000-B8576-C898-01
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