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3
3 Elements
3.7 Register
The special register is used to realize some special functions of PLC by specic values are written into. It is
a special unit used for data interaction between the user project and the PLC system project. For example,
in D8000, the time of the monitoring timer is initially set through the system ROM. To change the time, you
need to use the MOV instruction to write the target time in D8000.
Set the scheduled monitoring time to 200 ms
Refresh the monitoring timer
Besides, some special D registers are used to cache the system running status parameters. You can query
such registers to check the running parameters.
For characteristics of special data registers which can be retained upon power failure, see
“Appendix A
Allocation of Soft Elements SM, SD, D8000, and M8000” on page 704
.
The data register can be used to process numerical values of various types for control purpose. For
example, it can be used for dening the value of a timer or a counter, data computation and so on. The
instructions supporting D registers will be described in detail later.
3.7.2 Address Indexing Registers V and Z
Same as the general data register, the address indexing registers V and Z are 16-bit data registers for
numerical value reading and writing. There are 16 address indexing registers, namely, V0 to V7 and Z0 to
Z7.
The address indexing registers can be used in the same way as that of general data registers. Besides,
they can also be used in combination with the numbers or numerical values of other elements in the
operands of application instructions. Note that the numbers of elements of basic sequential control
instructions (such as LD, AND, and OUT) or STL instructions cannot be used together with the address
indexing registers.
The following gure shows how to use the V and Z registers to access data in 16-bit and 32-bit manners.
V0
(Most significant bits)
Z0
(Least significant bits)
Z1
(Least significant bits)
Z2
(Least significant bits)
Z3
(Least significant bits)
Z4
(Least significant bits)
Z5
(Least significant bits)
Z6
(Least significant bits)
Z7
(Least significant bits)
V1
(Most significant bits)
V2
(Most significant bits)
V3
(Most significant bits)
V4
(Most significant bits)
V5
(Most significant bits)
V6
(Most significant bits)
V7
(Most significant bits)
32-bit
The eight registers are
combined as follows in
case of 32-bit access manner
V
16-bit
Z
16-bit
V0 to V7: 8 points, Z0 to Z7: 8 points
16 independent registers are
used in case of 16-bit
access manner
Conventionally, to process elements in a 32-bit application instruction or a numerical value more than 16
bits (in 32-bit register manner), the V (higher bit) and Z (lower bit) registers are accessed simultaneously,
and the names of the specied registers must be Z0 to Z7. The address cannot be indexed even when the
higher bits of V0 to V7 are specied.
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