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Glossary
45
MODBUS RTU | SPI 3 | Trebing & Himstedt
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
number. Odd parity: the sum of all 1’s in a byte must be an
odd number. 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
control 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.
PROFIBUS
Pro
cess
Fi
eld
Bus
is an open Fieldbus system used to
network PROFIBUS compatible devices. PROFIBUS works
with three different protocols: PROFIBUS-DP (Decentral
Peripheral), PROFIBUS-FMS (Fieldbus Message
Specification), and PROFIBUS-PA (Process Automation).
PROFIBUS is standardized in EN 50 170.
Protocol
A set of rules and regulations which control the flow of
information in a communication system. The term protocol
can refer to either hardware or software.
Receive
The Fieldbus device receives a telegram from the DP
master through the SPI 3.
Receive channel
Data channel for data which the SPI 3 receives.
Remote peripheral
I/O device which is not directly integrated in the PLC CPU,
but is accessed remotely via the bus.
Response monitoring
If a slave is not accessed within the response monitoring
timeout, it switches automatically to a safe status by setting
all outputs to 0. The response monitoring timeout is
specified during parameter setting.