Siemens Simatic S7-400 - Manual (Page 171)

Digital Modules
4-49
S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07
Circuit as for active high or active low input
”1”
”0”
0V
– L+
U_s
”1”
U_s
DI_x
”1”
”0”
0V
L+
– L+
U_s
DI_xN
Channel x of the
DI 421 16 x 24/60 VUC
L+
U_s
Input threshold
Active high Active low
Figure 4-10 Circuit as for Active High or Active Low Input