Glossary
33
MODBUS
MODBUS RTU is implemented according to the Reference
Guide “Modicon PI-MBUS-300, Rev. D”.
Module
Selecting a module during device configuration determines the
configuration telegram and thus the size of the PLC I/O area.
MSB
M
ost
S
ignificant
B
it
Non-floating
With non-floating I/O devices, the reference potentials of control
circuits and power circuits are electrically interconnected and
are not galvanically isolated.
Non-isolated
With non-isolated I/O devices, the reference potentials of con-
trol circuits and power circuits are electrically interconnected.
Output byte
PLC address area which contains data which the DP master
sends to the DP slave.
Parameter
Variable used to specify the behavior of a device
Parameter master
When the system is booted, the parameter master passes pa-
rameter information to the DP slave. The parameter master can
write to and read from the slave and change the configuration of
the slave.
Parameter setting
To set the behavior of a DP slave and its modules.
Parameter telegram
Contains all parameters which can be set for a DP slave
Parity
Even parity: The sum of all 1’s in a byte must be an even num-
ber. Odd parity: the sum of all 1’s in a byte must be an odd num-
ber. The parity bit which can be 1 or 0 is used to create an even
or odd parity to allow detection of errors due to lost bits.
PII (Ger: PAE)
Process input image (PII)
PLC
Programmable logic controller, electronic controller whose con-
trol function is controlled by the program in its memory.
POI (Ger: PAA)
Process output image (POI)
Potential equalization
Electrical connection between conducting bodies to bring them
to an identical or practically identical potential and thus prevent
interfering or dangerous voltages between the bodies.
