I/O System S900
Communication Interface for PROFIBUS DP, CI920
28 3BDD010422R0101
configured default value (or last valid value) is transmitted instead. An input
value is invalid, if the I/O module cannot find a plausible measuring value,
e.g. in case of a line break or short-circuit. All channels of a module are
identified as invalid if the module is missing or an internal module error has
occurred. Output signals have no status at all.
Digital values
Digital input data can be transmitted with or without a measuring value status
(as configured). A set status bit identifies the respective channel as invalid. In
this case, the last valid value or the configured default value is transmitted
instead. A signal status bit and, if applicable, a measuring value bit is
assigned to every channel.
Analog values
Analog values are transmitted as Unsigned16 values in the Motorola format,
with 15-bit accuracy. The measuring value status can be transmitted in bit
position 0 or 15. Data are transmitted on channel 1 and higher. When a
channel is invalid, the status bit is set, and the last valid value or the
configured default value is transmitted instead of the measured value.
HART variables
HART variables are transmitted as FloatingPoint values. If the measured
value is invalid, NAN (Not A Number) is transmitted as the default value.
HART variables are transmitted after the data of the analog channels. The
following order is valid: from the lowest channel to the highest, from the
lowest variable to the highest.
Non-cyclic services DPV1
Functional principle
Besides cyclic data exchange, the DPV1 extension also permits non-cyclic
data exchange with a slave. Due to this fact, the I/O System S900 does not
need a local service or configuration interface. The organization, i.e. the
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