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3. Key Technical Specifications
- Model: D4-RSDC
- System: DirectLogic 405 (DL405) PLC
- Type: Serial Remote I/O Slave unit
- Power: 24 VDC (external or included supply depending on configuration)
- Communication: RS-485 via twisted-pair shielded cable
- Baud Rate: Up to 38.4 kbaud
- Maximum Distance: Up to 3300 ft (1000–1200 m) depending on cable and baud rate
- Compatibility: Used with D4-RM Remote Master module
- Maximum Slaves per Master: 7
- I/O Capacity: Depends on CPU (e.g., up to 512–1536 points system-wide)
- Mounting: Installs in any DL405 base
- Terminals: 5-pin terminal block for communication
4. Product Introduction
The AutomationDirect D4-RSDC is the 24 VDC serial Remote I/O Slave module for the DirectLogic 405 PLC family. It allows I/O bases to be located remotely from the CPU, significantly reducing field wiring costs.
The module is installed in a DL405 base populated with standard I/O modules and communicates with a D4-RM Remote Master (or the built-in remote port on certain CPUs) over a shielded twisted-pair RS-485 link. Multiple slaves can be daisy-chained. As a discontinued product, available units are typically New Surplus or residual stock.
D4-RSDC
D4-RSDC
5. Troubleshooting Quick Reference
| Symptom | Possible Cause | Relevance to this Part | Quick Check Method | Recommendation |
|---|---|---|---|---|
| No communication with master | Wiring, baud rate, or power issue | ✅ High | Check RS-485 wiring, termination, and 24 VDC power | Verify cable, polarity, and power supply |
| Slave not recognized | Address or configuration error | ✅ High | Confirm slave address and master configuration | Match settings in programming software |
| Intermittent communication | Noise or cable length | ✅ High | Inspect cable shielding and grounding | Use recommended cable (e.g., Belden 9841) and proper termination |
| I/O points not updating | Base or module fault | ✅ Medium | Check I/O modules in the remote base | Test local base operation first |
| Power LED off | 24 VDC supply missing | ✅ High | Measure voltage at power terminals | Restore correct 24 VDC supply |
If the issue persists, record master/slave configuration, cable length, and LED status before contacting support.
6. Frequently Asked Questions (FAQ)
Q: What is the difference between D4-RS and D4-RSDC?
A: D4-RS is the AC-powered remote slave. D4-RSDC is the 24 VDC-powered version.
Q: What master module is required?
A: The D4-RM Remote Master module (or the built-in remote I/O port on certain DL405 CPUs such as the D4-450).
Q: How many remote slaves can be connected?
A: Up to 7 slaves per remote master channel. Maximum number of masters depends on the CPU model.
Q: What cable should be used?
A: Shielded twisted-pair cable (minimum 24 AWG), such as Belden 9841 or equivalent. Maximum distance is approximately 3300 ft (about 1000–1200 m).
Q: Is the D4-RSDC still in production?
A: No. It has been discontinued by the manufacturer. Current availability is limited to New Surplus or residual stock.
Q: Why is pricing lower than current remote I/O systems?
A: This is a discontinued legacy module sold as New Surplus or residual stock. Pricing reflects remaining inventory rather than current production cost. All units are functionally verified before shipment. Standard warranty is typically 12 months.
Q: Can I mix D4-RSDC with newer AutomationDirect remote I/O?
A: No. It is specific to the DL405 serial remote I/O system and is not compatible with newer Ethernet-based or other remote I/O platforms.
