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3. Key Technical Specifications
| Parameter | Value |
|---|---|
| Type | Dual Cable S908 Remote I/O Processor |
| Cable Configuration | Dual coax (redundant) |
| Input Voltage | 5 V DC |
| Scan / Update Time | Approx. 3 ms + 1.3 ms/K of state RAM |
| Switchover Time (Hot Standby) | 13–48 ms on primary fault |
| Communication Interface | S908 RIO dual coaxial |
| LED Indicators | Ready, Comm Active, Comm Error |
| Operating Temperature | 0 °C to 60 °C |
| Storage Temperature | –40 °C to 80 °C |
| Humidity | 0–95 % non-condensing |
| Shock / Vibration | Industrial ratings (10 g shock, 5–500 Hz) |
| Weight | Approx. 1.1–1.81 kg (2.4–4.0 lbs) |
| Status | Discontinued by manufacturer |
4. Product Introduction
The Schneider Electric AS-S908-120RP is a dual-cable Remote I/O processor module for the Modicon 984 Series on the S908 network. It provides the interface between the main 984 controller and remote 800 Series I/O drops using redundant coaxial cables.
This module supports hot-standby configurations and is commonly used in plants that require high availability on legacy S908 RIO networks. Dual-cable operation improves noise immunity and allows continued communication if one cable path fails, making it a practical spare for existing dual-redundant installations.
5. Troubleshooting Quick Reference
| Symptom | Possible Cause | Relevance to this Part | Quick Check Method | Recommendation |
|---|---|---|---|---|
| No communication (Comm Error LED) | Cable fault, missing terminator, or processor failure | ✅ High | Verify both coax cables, terminators, and connectors | Repair cabling first; then test module |
| Ready LED off | Power or backplane problem | ✅ High | Measure 5 V DC at module; check rack power | Confirm supply and seating before replacement |
| Intermittent Comm Active | Loose F-connector or noise on one cable | ✅ Medium | Swap primary/secondary cables; inspect shields | Repair or replace the affected coax run |
| Hot-standby switchover fails | Configuration mismatch or defective unit | ✅ High | Verify primary/standby settings and cable integrity | Replace module if cabling and config are correct |
| Module not recognized by CPU | Address conflict or internal fault | ✅ High | Reseat module; check diagnostic LEDs | Replace module after confirming power and cabling |
If the fault continues, record all LED states, note which cable path is active, and capture any diagnostic information from the 984 controller for technical support.
AS-S908-120RP
AS-S908-120RP
6. Frequently Asked Questions (FAQ)
Q: Is the AS-S908-120RP still available new from Schneider?
A: No. It is discontinued. New-surplus and fully tested refurbished units are the current supply options for maintaining existing dual-cable networks.
Q: What does the “RP” suffix mean?
A: It identifies a specific hardware revision or configuration of the base AS–120 dual-cable processor. Functionally it is the dual-coax remote I/O driver.
Q: Can this module run in single-cable mode?
A: It is designed for dual-cable (redundant) operation. Single-cable use is possible in some setups but loses the redundancy benefit. Confirm your network design before installation.
Q: Does it support hot standby?
A: Yes. The module is hot-standby capable with switchover times typically in the 13–48 ms range when the primary path fails, provided the system is correctly configured.
Q: How do I verify the dual cables after replacement?
A: Check both F-type connectors for proper seating, confirm terminators are installed at the correct ends, and monitor the Comm Active / Comm Error LEDs while forcing a cable disconnect test if safe to do so.
Q: Can I hot-swap this processor?
A: No. Power down the affected RIO segment or the entire system before removal or insertion to avoid communication faults or hardware damage.
Q: Why choose a tested refurbished unit?
A: These processors undergo full dual-cable communication and diagnostic testing. They restore redundant drops quickly while carrying a warranty, avoiding the long lead times of scarce new-surplus stock.
