Schneider ASB881001 Latched Input Module

The Schneider ASB881001 captures and holds fast digital signals for Modicon PLC systems. This latched input module detects momentary pulses as short as 1 millisecond. You will find it in high-speed counting and event capture applications. It stores input states until the CPU reads them. Therefore, this unit prevents missed signals from fast machine operations.

This module measures 130 mm in height and 45 mm in width. Its depth reaches 100 mm for standard rack mounting. The unit weighs approximately 0.36 kilograms. It contains eight independent latching circuits with dedicated memory. Each channel uses an optocoupler for input isolation. Additionally, you get eight status LEDs for channel indication.

Key Technical Specifications

Parameter	Value
Manufacturer	Schneider Electric (Telemecanique)
Model	ASB881001
Product Type	Latched Input Module
Number of Inputs	8
Input Voltage	24 VDC
Input Current	7 mA per channel
Minimum Detectable Pulse	1 ms
Maximum Pulse Frequency	500 Hz
Latch Memory	8 bits (dedicated)
Input Impedance	3.4 k ohms
Isolation Type	Optocoupler (1500 VAC)
Height	130 mm
Width	45 mm
Depth	100 mm
Weight	0.36 kg
Latching Circuits	8 (independent)
Status LEDs	8 (yellow)
Energy Storage	≈ 150 µF (capacitive)
Power Consumption	180 mA @ 5 VDC
Operating Temperature	0°C to +55°C
Reset Method	Software command

Internal Architecture and Energy Storage

The Schneider ASB881001 stores minimal energy in its input filters. Small ceramic capacitors hold approximately 150 microfarads total capacitance. Each channel has a dedicated latch circuit with a D-type flip-flop. This flip-flop captures and holds the input state indefinitely. An optocoupler isolates each input from the internal logic. When a 24 VDC signal appears, the optocoupler triggers the flip-flop. The flip-flop output remains high until the CPU resets it. A common reset signal clears all eight latches simultaneously. The module includes debounce circuitry for noisy switch contacts.

Connection Interfaces and Wiring Details

You will find a 20-pin removable terminal block on the bottom face. This block accepts eight input wires plus two common returns. Connect the 24 VDC positive wire to the channel terminal. Connect the negative wire to the adjacent common terminal. Use 16 to 22 AWG copper wire for all field connections. The Schneider ASB881001 requires an external 24 VDC supply for inputs. Eight yellow LEDs light up when their respective latch stores a “1” value. Each LED remains lit even after the input signal disappears. A software command writes a “1” to the reset register to clear all latches.

Configuration and Installation Steps

You slide this module into any I/O slot of the Modicon rack. First, align the module with the upper and lower card guides. Then, push it firmly until the backplane connector seats completely. Secure the front panel with the two retaining screws. Connect all field wiring before applying power to the system. The Schneider ASB881001 requires no jumpers or dip switch settings. Use the PLC programming software to read the input register. After reading the captured states, execute a reset command immediately. The module draws 180 mA from the +5 VDC backplane supply. Test each channel with a pulse generator before connecting fast field signals.