Index Register [V And Z]; Numbers Of Index Registers; Functions And Structures - Mitsubishi FX3U Series Programming Manual

FX /FX Series Programmable Controllers
3U 3UC
Programming Manual - Basic & Applied Instruction Edition
4.10

Index Register [V and Z]

Index registers can be used as in the case of data registers. And they are special registers since they can
change the contents of device numbers and numeric values by program when combined with another device
number or numeric value in operands of applied instructions.

4.10.1 Numbers of index registers

The table below shows numbers of index registers (V and Z). (Numbers are assigned in decimal.)
When only "V" or "Z" is specified, it is handled as "V0" or "Z0" respectively.
FX /FX PLC
3U 3UC
*1. The characteristics related to protection against power failure cannot be changed by parameters.

4.10.2 Functions and structures

1. 16-bit type
Index registers have the same structures as data registers.
16 bits
V
V0 to V7:
8 points
2. 32-bit type
Make sure to use Z0 to Z7 when indexing a device in a 32-bit applied instruction or handling a numeric value
outside the 16-bit range.
V0 (high-order side)
V1 (high-order side)
V2 (high-order side)
V3 (high-order side)
V4 (high-order side)
V5 (high-order side)
V6 (high-order side)
V7 (high-order side)
Index type
V0 (V) to V7, Z0 (Z) to Z7
*1
16 points
16 bits
Z
Z0 to Z7:
8 points
This is because FX PLCs handle Z as the low-order side of a 32-bit
32 bits
register as shown in combinations of V and Z in the figure on the left.
Z0 (low-order side)
Even if V0 to V7 on the high-order side is specified, indexing is not
Z1 (low-order side)
executed.
When index registers are specified as a 32-bit device, both V (high-
Z2 (low-order side)
order side) and Z (low-order side) are referred to at the same time.
If a numeric value for another purpose remains in V (high-order side),
Z3 (low-order side)
consequently the numeric value here becomes extremely large, thus
Z4 (low-order side)
an operation error occurs.
Example of writing to 32-bit index registers
Z5 (low-order side)
Z6 (low-order side)
Z7 (low-order side)
Even if an index value in a 32-bit applied instruction does not exceed
the 16-bit numeric range, use a 32-bit operation instruction such as
DMOV instruction for writing a numeric value to Z as shown in the
figure on the left so that both V (high-order side) and Z (low-order
side) are overwritten at the same time.
FNC 12
K300 Z2
DMOV
K300→(V2,Z2)
4 Devices in Detail
4.10 Index Register [V and Z]
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