
B–63783EN/01
6. CONNECTION OF I/O UNITS TO
MACHINE INTERFACE
159
- Preventing malfunctions that may be caused by detouring current
When there are three or more matrix DI points, detouring current can
cause a nonexistent DI input to be falsely detected as existing.
As shown below, if KY01, KY03, and KY21 are closed
simultaneously, current detours through the path indicated with
arrows, thus causing a false input of *KY23 to be detected because of
a current path formed by a combination of common signal *KYC2 and
data signal *KYD3.
KY03 KY01
KY23 KY21
*KYC0
*KYC1
*KYC2
*KYC3
*KYD3
*KYD2
*KYD1
*KYD0
Two modes are available to prevent this malfunction. One should be
selected according to the user applications.
[Method 1]
D Ignoring all occurrences of three or more simultaneous inputs
Action : Make the *MNDI signal open (see item “D Key switch
addresses”)
NOTE
If there are two inputs and a third is added, all three are
ignored. When one of the three inputs is removed, two are
accepted.
[Method 2]
D Attaching detour prevention diodes to enable three simultaneous
inputs
Action : Connect the *MNDI signal (see item “D Key switch
addresses”) to 0V.
A diode must be connected in series with a switch, as shown below.
Detour prevention diode
*KYCn
*KYDn
D Mode selection