Function description
Operating Manual PSSu K F INC
1001688-EN-09
13
Functions
}
Period length measurement
or
}
Storing the counter status in latch memory after a latch pulse or zero pulse
}
Setting the counter status
The module transfers the data and status information to the head module via the module
bus. The choice of function and the function's configuration are defined via the system soft-
ware.
4.2.2.1
Functional inputs (G, L, S)
The single-pole inputs (G, L, S) are used for special functions. Inputs G and L may be con-
nected to external signal sources, e.g. to a higher order control system. If the gate signals
are generated by a non-safety-related device or if the gate inputs are connected, common
cause failures may arise. A failure mode and effects analysis must be carried out when wir-
ing the gate inputs.
}
Input G (gate input)
The counter is stopped with a 1 signal. The module ignores the counter pulses at the in-
puts until a 0 signal returns.
}
Input L (input for latch pulse)
At a rising edge, the module stores the current counter value in the latch memory. The
counter continues counting; it is not stopped by the latch pulse. The module transmits
the stored value to the head module. The period length measurement may be con-
figured as an alternative to the latch function.
}
Input S (status input)
The encoder's fault signal output can be connected to the status input. The module
transmits the input state to the head module with the status information.
4.2.2.2
Overflow
In both operating modes the counter can accept values from 0000 0000
H
to FFFF FFFF
H
.
}
With an underflow the value drops below 0000 0000
H
and the counter continues from
FFFF FFFF
H
.
}
With an overflow the value FFFF FFFF
H
is exceeded and the counter continues from
0000 0000
H
.
The overflow or underflow is signalled to the head module as status information.
The status information overflow is reset:
}
if the value again falls below 0000 0000
H
(underflow).
}
if 5555 0000
H
is exceeded (the lower third of the value range).
The status information underflow is reset:
}
if FFFF FFFF
H
is exceeded again (overflow).
}
if AAAA FFFF
H
is exceeded (the upper third of the value range).
