Siemens SIMATIC S7-400 Reference Manual page 108

Digital modules
4.8 Digital input module SM 421; DI 16 x DC 24 V (6ES7421-7BH01-0AB0)
Diagnostic message
Incorrect parameters
(module/channel)
Internal voltage failure Cannot be disa‐
Hardware interrupt
lost
Wire break (for each
channel)
Sensor supply miss‐
ing (also activated via
"No Load Voltage L+")
No load voltage L+
(for each channel
group)
Behavior when the input delay equals 0.1 ms or 0.05 ms and an error occurs
If you have set the following parameters:
● Input delay: 0.1 ms or 0.05 ms
● Reaction to error: "Keep Last Value" (KLV) or "Substitute Value" (SV)
● Set substitution value "1"
In the event of a fault on a channel that has a 1 signal, the following could occur:
● A 0 signal may be briefly output
● If configured, a hardware interrupt may be generated.
This occurs before the last valid value or substitute value "1" is output.
108
"Diagnostics" "Reaction to Error"
parameter parameter
Cannot be disa‐ Not relevant
bled
Substitute a value
bled (SV)
KLV
Cannot be disa‐ Not relevant
bled
Disabled -
Activated Substitute a value
(SV)
KLV
Disabled -
Activated Substitute a value
(SV)
KLV
Disabled -
Activated Substitute a value
(SV)
KLV
Input value of digital module
0 signal (module/all incorrectly config‐
ured channels)
Configured substitute value
Last read, valid value
Current process value
0 signal
Configured substitute value
Last read, valid value
0 signal
Configured substitute value
Last read, valid value
0 signal, if the contact is connected via
the sensor supply; process value for
the external sensor supply
Configured substitute value
Last read, valid value
S7-400 Automation System Module Data
Reference Manual, Ausgabe 11/2016, A5E00850736-08