GE IC695RMX128 Redundancy Memory Exchange Module – PACSystems RX3i

GE IC695RMX128 PACSystems RX3i Redundancy Memory Exchange Module — Synchronization Architecture for High-Availability Control Systems

The GE IC695RMX128 is a dedicated Redundancy Memory Exchange (RMX) module engineered for the GE PACSystems RX3i control platform. Its primary function within a redundant CPU pair is to maintain continuous, deterministic state synchronization between the primary and secondary CPUs across the RX3i universal backplane. When the primary CPU encounters a fault condition, the secondary CPU assumes control within a single scan cycle — a transition that is transparent to the field I/O and the supervisory SCADA layer. The IC695RMX128 provides 128 MB of dedicated exchange memory, sufficient to mirror the full logic data table, I/O image table, and system status registers of even the most data-intensive RX3i configurations.

Unlike software-based redundancy schemes that rely on Ethernet heartbeat packets and introduce variable latency, the IC695RMX128 operates over the RX3i high-speed backplane bus — a deterministic, time-sliced communication fabric that guarantees bounded transfer latency independent of network load. This architectural decision eliminates the jitter inherent in TCP/IP-based state replication and is the reason the IC695RMX128 is specified in SIL-rated and process-critical installations where switchover timing must be provably bounded.

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Technical Parameters

Hardware Logical Analysis

The IC695RMX128 occupies a dedicated slot in the RX3i universal backplane and communicates exclusively via the backplane’s internal high-speed bus rather than any external network medium. This is a deliberate hardware partitioning decision: by keeping the memory exchange path physically separate from the Ethernet-based SRTP and EGD channels used for SCADA communication, GE ensures that a network saturation event on the supervisory layer cannot degrade the synchronization fidelity between the redundant CPU pair.

Memory Architecture: The 128 MB exchange buffer is organized as a dual-port SRAM structure accessible by both the local backplane controller on the RMX module and the CPU’s memory bus. The primary CPU writes its current data table state into the RMX buffer at the end of each logic scan. The RMX module then transfers this snapshot to the secondary CPU’s corresponding memory space. The transfer is pipelined to overlap with the next scan execution, minimizing the synchronization window without extending scan time.

EMC Design: The module’s PCB layout follows GE’s standard RX3i EMC design rules, including ground plane stitching at the backplane connector interface, decoupling capacitors placed within 2 mm of each power pin on the SRAM array, and shielded traces on the high-speed data bus segments. These measures ensure the module meets the IEC 61000-4-4 (EFT/Burst) and IEC 61000-4-5 (Surge) immunity levels required for installation in industrial panel environments adjacent to variable-frequency drives and high-current contactors.

Redundancy Arbitration Logic: The IC695RMX128 participates in the RX3i redundancy arbitration protocol managed by the CPE CPU. The module monitors a set of health registers that the primary CPU updates each scan. If the primary CPU fails to update these registers within a configurable watchdog interval (typically 1–3 scan periods), the RMX module asserts a switchover signal on the backplane, which the secondary CPU interprets as authorization to assume the active role. This hardware-level watchdog is independent of the CPU’s application logic, meaning a runaway user program that consumes excessive scan time will still trigger a correctly timed switchover.

Thermal Management: The module operates within a 0–60 °C ambient range without forced air cooling when installed in a standard RX3i rack with adequate panel ventilation. The SRAM array’s power dissipation at full 128 MB utilization is within the thermal budget allocated per slot in the RX3i backplane power distribution specification, preventing localized hot spots that could accelerate SRAM wear.

System Integration Benefits

• Single-scan CPU switchover: The secondary CPU holds a fully synchronized copy of the primary’s data table at all times, enabling it to assume control within one logic scan cycle — typically 5–50 ms depending on program size — without any re-initialization sequence.
• Backplane-native synchronization path: Memory exchange occurs over the deterministic RX3i backplane bus, eliminating the variable latency and packet loss risk associated with Ethernet-based state replication schemes.
• Transparent I/O continuity: Field I/O modules connected to the backplane continue to receive output commands and report input states without interruption during a CPU switchover, because the I/O image table is fully replicated in the RMX buffer before the transition occurs.
• Scalable memory headroom: The 128 MB exchange capacity accommodates the full data table of the largest RX3i CPU configurations, including extended register arrays, symbolic variable tables, and system diagnostic data blocks, without requiring data table partitioning or selective synchronization workarounds.
• Diagnostic transparency: The IC695RMX128 exposes its operational status — synchronization state, transfer error counts, and watchdog status — through the RX3i system status registers, which are readable by Proficy Machine Edition and any SRTP-capable SCADA client. Operators can monitor redundancy health in real time without additional diagnostic hardware.
• Non-disruptive firmware updates: In a properly configured RX3i redundant pair, firmware updates to the primary CPU can be performed while the secondary holds control, and the RMX module re-establishes synchronization automatically after the update completes — a procedure that eliminates the planned downtime window traditionally required for controller maintenance.
• Plug-compatible with existing RX3i infrastructure: The IC695RMX128 installs into any standard RX3i universal backplane slot without backplane modification, making it straightforward to add redundancy capability to an existing non-redundant RX3i system during a scheduled maintenance window.
• Deterministic scan-time impact: The memory transfer cycle is designed to complete within a fixed time budget that the CPU scheduler accounts for, ensuring that adding the IC695RMX128 to a system does not introduce unpredictable scan time variation — a critical requirement in motion-coordinated and batch-sequenced applications.

Quality Assurance & Global Logistics

Every IC695RMX128 unit supplied by siemensplc.com is sourced through verified industrial distribution channels and carries full GE / Emerson Automation Solutions factory authenticity. Units are inspected against manufacturer batch codes, date codes, and PCB revision markings prior to dispatch. Anti-static ESD packaging with humidity indicator cards is used for all shipments to protect the SRAM array during transit.

Our logistics operation is based in Xiamen, China, with access to DHL Express, FedEx International Priority, and UPS Worldwide Expedited services. In-stock units are dispatched within 1–2 business days of order confirmation. Standard export documentation — commercial invoice, packing list, certificate of origin, and certificate of conformance — is provided with every shipment. For bulk procurement or project-based orders requiring phased delivery schedules, dedicated account management and volume pricing are available upon request.

All shipments comply with applicable export control classifications. HS code and ECCN documentation are available on request for customs pre-clearance purposes. DDP (Delivered Duty Paid) terms can be arranged for buyers in the EU, UK, and Southeast Asia who require a landed cost quotation.

A 12-month warranty covers all units against manufacturing defects and functional failure under normal operating conditions. Warranty claims are processed with a target replacement dispatch of 3 business days from confirmed fault diagnosis.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
Web: siemensplc.com
Location: Xiamen, China
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