Siemens SIMATIC S7-400 Reference Manual page 101

Connection and circuit diagram for SM 421; DI 16 x 24 V DC
24 V
2L+
24 V
2M
L+
24 V
Figure 4-3 Connection and circuit diagram for SM 421; DI 16 x 24 V DC
S7-400 Automation System Module Data
Reference Manual, Ausgabe 11/2016, A5E00850736-08
4.8 Digital input module SM 421; DI 16 x DC 24 V (6ES7421-7BH01-0AB0)
Front connector monitoring
INTF
1
EXTF
2
1L+
1L+
3
4
0
5
6
1
7
8
2
9
10
3
11
12
1Vs
13
14
4
15
16
5
17
18
6
19
20
7
21
22
1M
1M
23
1M
24
Monitoring of external auxiliary voltage 2L+
2L+
25
Monitoring of internal voltage
2L+
26
27
0
28
1
29
30
31 2
32
33 3
34
35
36
37
2Vs
38
4
39
40
5
41
42
6
43
44
7
45
46
47
2M
48
2M
M
Monitoring of external auxiliary voltage 1L+
Monitoring of internal voltage
1L+
1M
Short-circuit
protection
Monitoring of encoder supply 1Vs
1M
2L+
2M
Short-circuit
protection
Monitoring of encoder supply 2Vs
2M
Digital modules
1L+
2L+
101