Key Technical Specifications
- Product Model: PM856AK01 3BSE066490R1
- Manufacturer: ABB
- Processor: 32-bit RISC
- RAM: 16 MB
- Flash Memory: 8 MB
- Ethernet Ports: 2x RJ45 (10/100 Mbit/s, Redundant)
- Serial Ports: 2x RJ45 (COM3: RS-232, COM4: Isolated RS-232)
- Battery Backup: Internal Li-Ion (min. 2 weeks), External SB821/SB822 optional
- I/O Capacity: 1x S800 I/O cluster (12 units) via ModuleBus
- Execution Time: ~0.07 ms/bit (typical, verify with manual)
- Dimensions: 119 mm (W) × 186 mm (H) × 135 mm (D)
- Weight: ~1.1 kg (including TP830 and bus unit)
- Protection: IP20
Product Introduction
The ABB PM856AK01 3BSE066490R1 is a high-performance redundant CPU module for the AC 800M controller family, serving as the central processing unit in 800xA distributed control systems. It features dual 10/100 Mbit/s Ethernet ports for redundant communication networks and supports up to 12 S800 I/O units via the ModuleBus.Unlike the single-Ethernet PM851AK01, the PM856AK01 provides true network redundancy, ensuring continuous operation even if one network cable or switch fails. With 16 MB RAM and 8 MB Flash, it handles complex control strategies and large tag counts, making it the standard choice for critical process applications requiring high availability.
Installation & Configuration Guide
Preparation (10 min)
- Verify the 3BSE066490R1 ordering code matches your system configuration.
- Ensure the TP830 base plate and S800 I/O bus unit are correctly mounted.
- Wear an ESD wrist strap. (CPU modules are sensitive; static kills.)
Removal (5–10 min)
- Disconnect Ethernet and serial cables first to avoid port damage.
- Release the DIN rail latch and slide the PM856AK01 upward.
- Take a photo of the DIP switch/jumper settings before removal. Always.
Installation (10 min)
- Align the module with the TP830 backplane connector; push firmly until seated.
- Reconnect Ethernet cables to CN1 and CN2 (verify redundancy configuration).
- Connect COM3/COM4 as needed; ensure COM4 isolation is maintained if required.
Power-On & Test (10 min)
- Apply 24 VDC and observe the “OK” LED (solid green = normal).
- Check 800xA Control Builder for “Module OK” and no hardware faults.
- Verify redundant Ethernet switchover by disconnecting CN1 and confirming CN2 takes over.
Troubleshooting Quick Reference
| Symptom | Probable Cause | Action |
|---|---|---|
| “OK” LED Off | No 24 VDC or backplane fault | Measure voltage at TP830; check fuse |
| “OK” LED Blinking | Firmware mismatch or boot failure | Verify 3BSE066490R1 revision matches project |
| Redundancy Fault | Cable or switch failure | Check CN1/CN2 link LEDs; verify network config |
| Battery Low Alarm | Internal battery depleted | Replace internal Li-Ion or install SB821/SB822 |
| ModuleBus Comm Error | S800 I/O bus issue | Check bus unit LEDs; verify termination |
Dimensions, Mounting & Wiring Notes
- Dimensions: 119 mm (W) × 186 mm (H) × 135 mm (D)
- Mounting: DIN rail (TP830 base plate required)
- Terminal Notes: Ethernet via RJ45 (CN1, CN2); Serial via RJ45 (COM3, COM4)
- Wiring Note: Use shielded Ethernet cable (Cat5e or better); ground shield at panel end only
FAQ
What’s the difference between PM856AK01 and PM851AK01?
The PM856AK01 has two Ethernet ports for redundancy; the PM851AK01 has only one. If your system requires redundant communication, you must use the PM856AK01.Can I replace a PM851AK01 with this module?
Yes, but you must update the hardware configuration in Control Builder and verify the firmware version. The PM856AK01 is a direct functional upgrade, but the project must be recompiled and downloaded.Is this module new or refurbished?
This unit is refurbished and tested. We verify origin via serial number traceability and perform full functional testing on an AC 800M test rack. It is function verified under test conditions.How long does the internal battery last?
The internal Li-Ion battery provides a minimum of 2 weeks of RAM backup. For longer retention (up to 8 months), install an external SB821 battery module.Do you provide a test report?
Yes. Every PM856AK01 3BSE066490R1 ships with a test report documenting Ethernet connectivity, serial port functionality, and memory integrity.Can I hot-swap this CPU?
No. CPU modules must be replaced during a maintenance window with the backplane powered down. Hot-swapping a CPU will cause a system crash and potential data loss.
