The CI851K01 is a Profibus-DP communication interface module kit designed by ABB for the AC 800M controller hardware platform within the 800xA control system series. This product belongs to the Communication Modules category of the AC 800M hardware series and is specifically applicable to AC 800M Hardware 2.1 (SB2) and AC 800M Hardware 3.0 versions. Its core function is to provide reliable, high-speed data communication capability between the AC 800M controller and field devices, remote I/O, or external gateways based on the Profibus-DP protocol. It serves as a crucial bridge for integrating Distributed Control Systems (DCS) with field-level devices.
The CI851K01 is essentially a kit containing two core components: the CI851 (Communication Interface Unit) and the TP851 (Mounting Baseplate, width = 60 mm). It is primarily used to connect devices such as S200 I/O to the AC 800M controller via a Profibus-DP network. This product is positioned as a communication solution for industrial automation, particularly suitable for maintaining, repairing, or performing limited functional upgrades on existing early-generation AC 800M systems. It is important to note that, according to the EU RoHS 2 (2011/65/EU) directive, this part is non-compliant. It is intended solely as a spare part for systems placed on the market before July 22, 2017, and may only be ordered for repair, reuse, updating of functionalities, or upgrading of capacity. For new installations, ABB recommends using its successor products, the CI854AK01 or CI854BK01.
2. Product Composition and Physical Characteristics
The CI851K01 kit consists of the following two parts:
CI851 Communication Interface Unit: This is the core processing part of the module, containing the CEX-Bus logic, a communication processor, and a DC/DC converter. This converter draws power from the +24V DC supply via the CEX-Bus and generates the required operating voltages for the module's internal circuitry. The CI851 unit is responsible for handling internal communication with the controller and the Master communication protocol on the Profibus-DP network.
TP851 Mounting Baseplate: This is a 60 mm wide baseplate used to mechanically secure and electrically connect the CI851 unit to a DIN rail. The TP851 baseplate integrates a crucial 9-pin female D-type (DB9 female) connector for connecting the Profibus-DP fieldbus cable. Additionally, the baseplate is equipped with a pre-set two-letter Alpha code mechanical locking device. This design effectively prevents incorrect unit types from being mistakenly installed on this baseplate, ensuring system hardware compatibility.
Physical Characteristics:
Dimensions (Single Module): Width 59 mm × Height 185 mm × Depth 127.5 mm.
Weight: The net weight of the entire CI851K01 kit (including CI851 and TP851) is approximately 0.3 kg, with a total packaged weight of about 700 g (1.5 lb).
Protection Rating: IP20 (according to EN60529/IEC 529 standards), suitable for dry electrical cabinet environments, providing basic finger protection.
Mounting Method: Standard DIN-rail mounting, simple and fast.
Selling Unit: Piece, with a Minimum Order Quantity of 1 piece.
3. Key Functions and Features
Profibus-DP Master Function: The CI851 operates as a Class 1 Master, actively polling slave devices on the network for stable cyclic data reading and writing.
High-Performance Communication: Supports a wide range of baud rates from 9.6 kbit/s to 12,000 kbit/s, allowing flexible configuration based on network scale and real-time requirements. Under optimal conditions, the minimum communication cycle time can be as low as 1 ms.
Robust Network Expansion Capability: Each Profibus-DP port can theoretically connect up to a maximum of 124 nodes (using repeaters). Up to 32 slave devices can be directly connected on a single segment, meeting the needs of medium-scale systems.
Galvanic Isolation: The module provides electrical isolation on the Profibus-DP interface side, enhancing system immunity to interference and safety, helping to protect the controller-side circuitry from potential differences or noise from the field side.
Intuitive Status Indication: The module front features multi-color LED indicators, including:
Run / Green: Indicates the module is operating normally.
Fault / Red: Indicates the module has detected an internal or communication error.
Rx/Tx / Yellow: Flashes to indicate data transmission between the module and the Profibus-DP network.
RTS / Yellow: Flashes to indicate the module is requesting to send data.
Plug-and-Play Design: Simplified installation and connection via the DB9 connector and mechanical code lock on the TP851 baseplate, reducing the risk of misoperation.
CEX-Bus Power Supply: The module receives +24V DC power from the AC 800M controller's CEX-Bus, eliminating the need for an external independent power supply and simplifying system wiring.
4. Installation and Connection
Installation Steps:
Mount the TP851 baseplate onto the standard DIN rail in the control cabinet. Refer to the AC 800M hardware manual chapter on "Mounting AC 800M Units onto DIN-Rail" for specific instructions.
Align the CI851 communication interface unit with the guide slots on the TP851 baseplate and press down firmly until the mechanical locks engage, ensuring secure installation. The mechanical code lock prevents installation of incorrect unit types.
Profibus-DP Connection:
Use shielded twisted pair cables compliant with Profibus-DP standards.
Properly ground the cable shield to minimize electromagnetic interference.
Connect the cable to the 9-pin D-type connector on the TP851 baseplate. Pin assignment is as follows:
| Pin | Designation | Description |
| 1 | Shield | Shield/Protective Ground |
| 2 | - | Not Used |
| 3 | B-line | Receive/Transmit Data B-line |
| 4 | RTS (TTL) | Indicates direction (Request To Send) |
| 5 | GND Bus | Bus Ground |
| 6 | +5 V Bus | For terminating resistors |
| 7 | - | Not Used |
| 8 | A-line | Receive/Transmit Data A-line |
| 9 | - | Not Used |
Terminating Resistors: The Profibus-DP network must be terminated with resistors at the two physically outermost nodes to ensure signal integrity. ABB recommends using connectors with built-in termination resistors, ensuring the bus remains correctly terminated even if the connector is fully disconnected from the unit.
For detailed fieldbus installation specifications, recommended certified devices, and components, please refer to the relevant fieldbus documentation and manual appendices.
5. Application Guidance and Fault Finding
Application Scenarios:
The CI851K01 is primarily used to connect remote I/O stations (e.g., S200 I/O) via a Profibus-DP network. Simultaneously, it can also integrate field devices supporting the Profibus-DP protocol, such as smart instruments and drives, into the AC 800M control system through an external gateway on Profibus-DP, enabling process data acquisition and control command distribution.
Limitations:
Non-Redundant Design: The CI851 itself does not provide unit-level hardware redundancy.
No Hot Swap Support: The CI851 module cannot be directly plugged/unplugged or replaced while the system is running.
Firmware Upgrade Restriction: Online firmware upgrade operations are not allowed in system configurations containing a CI851 module.
Obsolete/Replaced: The CI851 has been superseded by the more feature-rich and potentially higher-performance CI854 series communication interface modules. The new products may offer enhancements in functionality, redundancy support, etc.
Fault Finding Guide:
The table below lists common fault phenomena, their possible causes, and corrective actions:
| Fault Phenomenon | Possible Cause and Corrective Action |
| Neither Run (Green) nor Fault (Red) LEDs are ON | 1. The CI851 board is in the process of being re-started or configured. Allow time for this to finalize.
2. If the condition persists for a long time, and all other units on the CEX-Bus also have non-illuminated LEDs:
- Check that a valid hardware configuration including the CI851 is downloaded to the controller.
- Check the CEX-Bus fuse inside the PM8xx processor unit.
- Initiate a reset signal (INIT) from the PM8xx processor unit.
- Replace the CI851 unit. |
| Fault (Red) LED is steadily ON | A unit error is detected. Please check:
1. All Profibus-DP cables and connectors for damage, looseness, or incorrect termination.
2. Repair as necessary. |
| Run (Green) LED is flashing | 1. Check if the relevant slave devices are sending data.
2. Check if the CI851 board is in the process of being restarted or configured. If so, allow time for this to finalize.
3. If the condition persists:
- Halt the application program and initiate a restart.
- Replace the CI851 board. |
| Communication interruption or abnormality | 1. Check if the baud rate setting matches all devices on the network.
2. Check if the network topology and cable length comply with Profibus-DP specifications.
3. Verify that terminating resistors are correctly installed at both ends of the network.
4. Check for sources of electromagnetic interference and ensure the shield is properly grounded at one end. |
