The SC520 is a critical component of the ABB Advant® OCS (Open Control System) within the Advant Controller 450 series. It is an intelligent submodule carrier equipped with a local Central Processing Unit (CPU), identified by the model number 3BSE003816R1. This module serves as a key hardware platform within the Advant Controller 450 architecture, specifically designed to house and operate various communication submodules, thereby significantly expanding the controller's communication capabilities and system integration scope.
Within the modular system of the Advant Controller 450, the submodule carrier acts as a bridge connecting the controller core (Processor Module PM511) to the external world (such as other control systems, operator stations, fieldbus devices, and third-party equipment). The SC520 is not merely a passive mechanical carrier but an intelligent platform with independent processing capabilities. Its integrated local CPU can offload communication processing tasks from the main processor, executing specific communication protocols and data exchange functions. This significantly enhances the overall control system's performance, real-time responsiveness, and reliability.
The SC520 is typically installed within the controller subrack of the Advant Controller 450. It provides power, data bus connections, mechanical support, and a cooperative processing environment for various communication interface submodules (e.g., C1531, C1532Vxx, C1543, C1570). It supports "hot-swap" functionality, facilitating maintenance and module replacement during system operation. Its design adheres to the stringent requirements of industrial environments, featuring high reliability, excellent electromagnetic compatibility, and ease of diagnosis and maintenance.
II. Primary Functions
The SC520 Submodule Carrier boasts rich and powerful functionalities, primarily demonstrated in the following aspects:
1. Hardware Support and Carrier Functionality:
Modular Carrier: The core function of the SC520 is to provide physical mounting slots and electrical connections for up to two communication submodules. It connects to the controller's main processor module (PM511) via a backplane bus (e.g., Futurebus+).
Power Management and Distribution: The module is responsible for receiving +5V and +24V DC power from the system supply and distributing it stably and reliably to its own circuitry and the submodules it hosts. Its design accounts for the varying power consumption of different submodules, ensuring stable power supply.
Hot-Swap Support: In configurations where the design permits, it supports the installation or removal of submodules, and in some cases the carrier itself, without shutting down system power. This greatly enhances system maintainability and availability.
Thermal Design: The module's construction considers heat dissipation needs, ensuring stable operation for itself and its hosted submodules within rated temperature ranges.
2. Communication Expansion and Protocol Processing:
Multi-Protocol Communication Hub: By inserting different communication submodules, the SC520 enables the Advant Controller 450 to support dozens of industrial communication networks and protocols, including but not limited to:
Control Network: MasterBus 300 / 300E (via CS513 submodule) for real-time data exchange between the controller and high-level nodes like Advant Station operator stations and Information Management Stations.
Fieldbus: MasterFieldbus (via C1570 submodule) for connecting S400 I/O units or other compatible devices; Advant Fieldbus 100 (requires other interfaces); PROFIBUS-DP (via C1541V1 submodule); LONWORKS Network (via C1572/C1573 submodules).
Serial Communication: Provides RS-232-C/V.24 interfaces (via C1531 submodule) for connecting printers, local operator stations (MasterView 320), or communicating with external computers via the EXCOM protocol.
Multi-Vendor Interface (MVI): Supports various standard industrial protocols such as RCOM, MODBUS, Siemens 3964(R), etc. (via C1532Vxx or C1534Vxx submodules), as well as a free-programmable interface for user-defined protocols (via C1535/C1538 submodules).
Load Sharing via Local CPU: This is the core advantage of the SC520. For certain high-load or highly time-critical communication tasks (e.g., MasterBus 300/300E network communication), the option exists to execute the communication protocol stack processing on the SC520's local CPU instead of the main controller CPU (PM511). This "executed in slave CPU" mode can significantly reduce the load on the main CPU (documentation indicates lower main CPU load for data sending/receiving when using SC520 compared to the SC510 carrier without a local CPU). This frees up main CPU resources for executing critical control logic, algorithms, and process I/O handling, thereby optimizing overall system performance.
Redundant Communication Support: The SC520 and its submodules can be configured as part of redundant communication links, such as building redundant MasterBus 300 networks or Advant Fieldbus 100 networks, enhancing system communication reliability.
3. System Integration and Diagnostic Functions:
Seamless System Integration: As part of the standard Advant OCS architecture, the SC520 is fully compatible with system software (e.g., program modules like QC07-BAS41). Its hosted submodules are automatically recognized and configured within the system. Communication functions can be easily programmed and accessed via corresponding PC elements in AMPL (ABB Master Programming Language), such as COM-STAT, DSP-R, DSP-S, MFB-IN, MFB-OUT, etc.
Status Monitoring and Diagnostics: The module features comprehensive diagnostic capabilities. The status of communication links or the submodule itself can be quickly identified through the system status display (viewable on engineering or operator stations) and LED indicators on the module's front panel (e.g., Run/Fault lights). System Messages provide detailed reports on hardware errors (e.g., initialization failure, checksum error, module missing), aiding maintenance personnel in troubleshooting.
Configuration Flexibility: Multiple SC520 carriers can be installed within a controller subrack as needed, each hosting different combinations of communication submodules. This allows for the construction of communication topologies that meet the demands of complex project requirements.
III. Working Principle and Architecture
The working principle of the SC520 is based on an advanced distributed processing architecture and modular design philosophy. Its workflow and internal collaboration mechanism are as follows:
1. Hardware Architecture and Bus Interaction:
The SC520 itself is a complex printed circuit board, with its core being the integrated local microprocessor (CPU). This processor is tightly connected to the main processor module PM511 via a high-speed parallel bus (based on the Futurebus+ standard in the Advant Controller 450). This bus is the "highway" for data and command exchange.
Data Exchange: The main CPU (PM511) uses this bus to write data packets, control commands, or configuration parameters destined for external networks into the shared memory area of the SC520 and its submodules. Conversely, the local CPU on the SC520 writes data, status information, or event reports received from external networks into memory areas accessible by the main CPU via the same bus.
Interrupts and Coordination: Both parties can notify each other of new tasks or pending data via interrupt mechanisms, enabling efficient collaborative work.
2. Role of the Local CPU and the "Load Sharing" Principle:
The local CPU of the SC520 acts as a "communication coprocessor" or "intelligent gateway." Its operating mode primarily depends on the type of communication submodule installed and the system configuration:
Protocol Processing Mode: For certain communication submodules (e.g., a CS513 MasterBus 300 module configured for "executed in slave CPU" mode), the processing of the lower to middle layers of the communication protocol stack (e.g., frame encapsulation/decapsulation, link management, error detection, media access control) is handled entirely by the SC520's local CPU. The local CPU independently manages the network interface, processes the raw data stream on the network, and only passes the extracted valid application-layer data (or events) to the main CPU via the backplane bus. Conversely, it packages application data received from the main CPU into frames compliant with the network protocol and transmits them. The advantages of this mode are:
Reduced Main CPU Load: Offloads time-consuming and periodic communication protocol processing tasks from the main CPU, allowing it to focus on control task cycles with higher determinism requirements.
Improved Real-Time Performance: The local CPU can respond to network events more promptly, reducing communication delays caused by main CPU task congestion.
Enhanced System Performance: Allows the system to handle denser network communication traffic without impacting control performance.
Interface Management/Pass-Through Mode: For other submodules (e.g., C1531 RS-232 interface), the local CPU may primarily handle interface initialization, parameter configuration, data buffering, and flow control. The parsing of data content might be performed by software (e.g., EXCOM drivers) running on the main CPU. Even so, the presence of the local CPU simplifies the driver burden on the main CPU.
3. Collaboration with Submodules:
The SC520 provides a standardized electrical and logical interface for each submodule slot. The local CPU communicates with each submodule via an internal bus or dedicated interface for initialization, control, and status monitoring.
Initialization and Configuration: During system startup, the main CPU instructs the SC520's local CPU via the backplane bus to power on, perform self-tests, and configure parameters for each submodule.
Task Distribution and Data Routing: The local CPU routes data to the correct submodule based on the communication destination. For example, data destined for the MasterBus 300 network is handed to the CS513 submodule, while data for a serial printer is sent to the C1531 submodule.
Fault Isolation: If a submodule fails, the SC520's local CPU can detect and isolate it, preventing the fault from affecting other submodules or the backplane bus, and report it to the main CPU via diagnostic mechanisms.
4. Role in System Redundancy:
In systems configured with redundant Advant Controller 450 units (dual PM511) or redundant communication networks, the SC520 can support redundancy for critical communication paths.
Redundant Communication Interfaces: Two identical communication submodules can be installed (e.g., two C1522A for redundant Advant Fieldbus 100), each connected to independent physical networks. The SC520's local CPU can manage the status of both interfaces, automatically or manually switching to the backup link if the primary fails.
Coordination with Redundant CPUs: In redundant processor configurations, the two PM511 main CPUs typically share critical communication resources. The SC520 and its submodules must be accessible and manageable by both main CPUs, ensuring that all external communication connections can be seamlessly transferred or quickly re-established during a primary/backup switchover.
5. Software and Firmware Integration:
The operation of the SC520 and its local CPU relies on firmware and system software support. This software is typically integrated into the Advant Controller 450's basic system program module (QC07-BAS41). During system startup, while loading its own system software, the main CPU also loads the necessary firmware and drivers into the SC520's local CPU. At the application programming level, engineers do not program the SC520 directly. Instead, they utilize the powerful communication capabilities provided by the SC520 indirectly by configuring the controller system data and programming the corresponding communication PC elements.
