Digital Modules
4-46 S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07
Technical Specifications of the SM 421; DI 16 24/60 VUC
Programming package
Associated programming
package As of STEP 7 V 2.0
Dimensions and Weight
Dimensions W H D
(in millimeters) 25 290 210
Weight Approx. 600 g
Data for Specific Module
Number of inputs 16
Length of cable
•Unshielded
input delay
– 0.5 ms
– 3 ms
– 10 / 20 ms
Max. 100 m
Max. 600 m
Max. 600 m
•Shielded line length 1000 m
Voltages, Currents, Potentials
Number of inputs that can be
triggered simultaneously 16
Isolation
•Between channels and
backplane bus Yes
•Between the channels Yes
– In groups of 1
Permitted potential difference
•Between the different
circuits 75 VDC, 60 VAC
Insulation tested with
•Channels against
backplane bus and load
voltage L+
1500 VAC
•Channels among one
another 1500 VAC
Current consumption
•From the backplane bus Max.150 mA
Power dissipation of the
module Typ. 8 W
Status, Interrupts, Diagnostics
Status display Green LED per
channel
Interrupts
•Hardware interrupt
•Diagnostic Interrupt
Parameters can be
assigned
Parameters can be
assigned
Diagnostic functions Parameters can be
assigned
•Group error display
– For internal fault Red LED (INTF)
– For external fault Red LED (EXTF)
•Channel error display (F) None
•Diagnostic information can
be displayed Possible
Monitoring for
•Wire break I > 0.7 mA
Substitute value can be applied No
Sensor Selection Data
Input voltage
•Rated value 24 VUC to 60 VUC
•For signal “1” 15 to 72 VDC
-15 VDC to -72 VDC
15 to 60 VAC
•For signal “0” -6 VDC to +6 VDC
0 VAC to 5 VAC
Frequency range 47 DC/AC to 63 Hz
Input current
•At signal “1” Typ. 4 mA to 10 mA
Input characteristic curve Similar to IEC 61131 1)
Connection of two-wire BEROs
•Permitted bias current
Possible
Max. 0.5 mA to 2 mA2)
Time, Frequency
Internal preparation time for
•Only hardware interrupt
enable Max. 450 s
•Enable hardware and
diagnostic interrupts Max. 2 ms
Input delay
•Parameters can be
assigned Yes
•Rated value 0.5/3/10/20 ms
Values go into cycle and response times.
Sensor Circuit
Resistance circuit of the sensor
for wire break monitoring
•Rated voltage 24 V
(15 V to 35 V)
•Rated voltage 48 V
(30 V to 60 V)
•Rated voltage 60 V
(50 V to 72V)
18 kΩ
39 kΩ
56 kΩ
1) IEC 61131 does not specify any data for UC

modules. The values have been adapted as much

as possible to IEC 61131.

2) Minimum closed-circuit current is required for wire

break monitoring.