Siemens S7-300 Installation And Operating Manual page 336

Glossary
HART protocol
The → HART protocol is the industry standard for extended communication with → HART
field devices. It includes → HART commands and → HART replies.
HART replies
The HART field device transmits data at the request of the master. These data are
measurement results or manipulated variables or values of → HART parameters. A HART
reply always contains a status information, i.e., the → HART status bytes.
HART signal
Analog signal on a current loop of 4 - 20 mA, with which the sine waves for the → HART
protocol, 1200 Hz for binary "1" and 2200 Hz for binary "0", are modulated up using →
frequency shift keying.
HART status byte
Status information that consists of the first and second status bytes of the → HART reply and
that the HART field device uses to provide information regarding the → HART
communication, the receipt of the → HART command and the device status.
HART transfer area
Area of data records that is specified in the HART analog modules for writing HART
commands and reading HART replies. The HART transfer area consists of data records. A
separate area of data records is assigned to each → client and is used by the → server to
exchange data with the client.
HCF
→ HART Communication Foundation
IO Controller
-> PROFINET IO Controller
IO Device
-> PROFINET IO Device
Light period
Light periods develop in the course of complete bit pattern tests. The fail-safe output module
returns test-specific "1" signals to the inactive output (when output signal = "0"). This briefly
enables the output (= "light period"). A sufficiently slow actuator does not respond to this
signal and remains deactivated.
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Fail-safe signal modules