User Manual

Logical I/O blocks
Value objects for operation
19
CM110664en_07 263 | 351
19.5 Value objects for operation
To simplify operation, use the value objects BVAL_OP, AVAL_OP and MVAL_OP. The blocks are specifically
intended for the operation of setpoints via BACnet clients. They do not require a manual override from the
operator unit. Value objects look like all other blocks, and can be connected with other blocks. The blocks
do not include alarm generation or runtime totalization.
19.6 Addressing the I/O blocks
Hardware independence
Logical I/O blocks allow the standardization of the inputs and outputs irrespective of the hardware. The
relationship between a given logical I/O and its physical equivalent is established by assigning the address
of the I/O system concerned.
This independence has the advantage that the functions of the block, as defined by the BACnet standard
and the specific Desigo PX enhancements, do not change. The number of different I/O systems or physical
I/Os can be expanded freely.
Identical compound libraries
Another advantage is that the compound libraries are always identical. In the engineering phase, they are
adapted to the I/Os in the project by assigning the appropriate addresses. The process values (0…10V,
0…25mA, signal contacts, etc.) from the connected field devices are registered directly at the physical
inputs. The physical outputs deliver the process values (0…10V, switching stages 0 / I /II / III, etc.) directly
to the connected field devices.
The process values are transmitted in the form of raw data via the relevant medium (e.g., PPS2); the
conversion of the raw value takes place within the block.
Rules:
● Values from the plant are measured and processed in Input blocks (Analog, Binary or Multistate).
● Values to the plant are processed and transmitted by Output blocks (Analog, Binary or Multistate).
I/O systems
To enable the process value of the logical I/O block to be allocated to the appropriate physical I/O, the
relevant address must be assigned. The address is assigned as follows:
● Via automated assignment by the Point Configurator to the CFC
● Direct allocation to the I/O block in Xworks Plus (XWP)
The logical I/O blocks are designed for universal use in various I/O systems. The specific address
structures and hardware definitions are determined by the I/O system, e.g., the failsafe control value for
the island bus.
T
R
I/O module
Physical
input
Program in XWP
Block
AI
Island bus
10664-24Z01en
R
Logical
input
Logical
output
I/O module
Physical
output
BO
Island bus