IP 240
Position Decoding
7.2.5
Forcing the IP Outputs
You can use control bits DAnF and DAnS (n=1 for digital output 1 or n=2 for digital output 2) to
indicate whether output D1 or D2
•
is to be enabled for actual value-dependent switching by the IP
(if so, set DAnF to 0 and DAnS to 1 in DL17)
•
is to be set without regard to the actual value
(if so, set DAnF to 1 and DAnS to 1 in DL17)
•
is to be reset without regard to the actual value
(if so, set DAnF to 0 and DAnS to 0 in DL17).
After modifying control bits DAnF and DAnS in the DB, you must invoke control FB 170 and
initialize it for function 2 ”Write control bits”. The FB then transfers the control bits to the IP.
Status bits DA1 and DA2 reflect the current state of the outputs.
7.2.6
Monitoring of Signal Acquisition
Status bit DRBR (wirebreak) is set when a wirebreak or short-circuit is detected on the lines for
encoders with symmetrical signals. This bit remains set on the IP until the problem has been
rectified.
Status bit NPUE (zero point monitoring) is set when the IP detects that the number of encoder
pulses between two zero marks (Z signal) is not divisible by 4 or 5 without a remainder. This
method of zero mark monitoring makes it possible to detect spurious or missing pulses. Zero mark
monitoring is initiated on the IP 240 only when a reference point approach was terminated with
synchronization.
Zero mark monitoring is possible only when the timing of the encoder signals conforms to the
specifications discussed in Chapter 13 ”Encoder Signals”. In addition, when you configure the
channel you must specify whether the number of pulses between two Z signals is divisible by 4 or
by 5 (without a remainder). The IMP parameter in configuration FB 169 is provided for this
purpose.
The evaluation of zero mark monitoring must be disabled if the required encoder timing conven-
tions are not observed or if the number of encoder pulses between two Z signals is divisible by
neither 4 or 5.
The IMP parameter may be initialized to the following values:
IMP = 0
No evaluation of zero mark monitoring.
IMP = 10
The number of encoder pulses between two Z signals is divisible by 5 without a
remainder.
IMP = 16
The number of encoder pulses between two Z signals is divisible by 4 without a
remainder.
The module firmware scans for wirebreak and zero mark monitoring in every cycle. If a fault is
detected,
•
the DRBR or NPUE bit is set on the IP,
•
the comparison of actual value with track limits is suspended, and
•
the SYNC bit ( Section 7.2.9) is reset.
EWA 4NEB 811 6120-02a
7-13
