1769-SDN — Compact I/O DeviceNet Scanner Module

The 1769-SDN is a DeviceNet scanner module that slots directly into a 1769 Compact I/O bus and acts as the DeviceNet master for a connected network of field devices. From the controller's perspective it presents itself as a standard I/O module — input and output data from all DeviceNet slave devices map into the scanner's I/O image, which the CompactLogix program reads and writes like any other I/O point.

The module manages the scan cycle, polls each node, and handles the DeviceNet protocol overhead autonomously. The controller program doesn't need to manage DeviceNet communication directly — it just works with the mapped data. This makes integration of DeviceNet-connected drives, valve banks, and smart sensors straightforward without adding complexity to the ladder or structured text program.

Specifications

Parameter	Value
Part Number	1769-SDN
Platform	Compact I/O (1769)
Network	DeviceNet (CAN-based, ISO 11898)
Role	Master (Scanner)
Max Slave Nodes	63
Baud Rates	125 kbps, 250 kbps, 500 kbps
I/O Data per Node	Up to 255 bytes input / 255 bytes output
Scanner I/O Image	Up to 124 words input / 124 words output
Explicit Messaging	Supported (MSG instruction)
Configuration	RSNetWorx for DeviceNet
Backplane Current (5V)	375 mA
Backplane Current (24V)	75 mA
Operating Temperature	0°C to 60°C
Standards	DeviceNet Spec v2.0, UL 508, CE

How It Fits Into a DeviceNet System

DeviceNet uses a trunk-and-drop topology. The 1769-SDN connects to the trunk cable via its 5-pin open-style connector, which carries both the CAN signal pair and the 24V network power. Field devices — drives, I/O blocks, proximity switch blocks, valve manifolds — connect as slave nodes at drops along the trunk.

The scanner polls each slave node cyclically. Input data (status, feedback values) flows from slave to scanner; output data (commands, setpoints) flows from scanner to slave. The scan cycle time depends on the number of nodes, baud rate, and data size per node. At 500 kbps with a modest number of nodes, scan times well under 10 ms are typical.

The 1769-SDN also supports explicit messaging via the MSG instruction in the controller program. This allows on-demand reads and writes to device parameters — reading a drive's fault code, adjusting a sensor threshold — without consuming cyclic scan bandwidth.

RSNetWorx for DeviceNet is required to configure the scanner's scan list — the list of nodes the scanner polls, their data sizes, and their addresses. This offline configuration is uploaded to the module separately from the controller program. Keep the RSNetWorx project file version-controlled alongside the PLC program.

Node Address and Baud Rate

Every device on the network — including the scanner itself — needs a unique MAC ID (node address) between 0 and 63. Address 0 is conventionally reserved for the scanner/master. Slave addresses are set on the device itself, either via rotary switches, DIP switches, or software depending on the device type.

All devices on the same network must run at the same baud rate. 500 kbps is the most common choice for modern installations; 125 kbps is used where cable length exceeds the 500 kbps limit (maximum trunk length drops from 100 m at 500 kbps to 500 m at 125 kbps).

Things That Catch People Out

Network power: the 1769-SDN does not power the DeviceNet network. A separate 24V DeviceNet power supply must be wired onto the trunk. Network power is required for nodes to communicate regardless of their own local supply.
Termination resistors: 121 Ω termination resistors must be fitted at both ends of the trunk. Missing termination is one of the most common causes of intermittent DeviceNet communication faults.
Scan list mismatch: if the physical network changes (a node is added, removed, or has its address changed), the scan list must be updated in RSNetWorx and re-uploaded to the scanner. The scanner will fault on nodes that are in the scan list but absent from the network.
I/O image mapping: the 124-word input/output image is shared across all slave nodes. Large nodes with lots of data consume more of this space — check available image size before adding large I/O blocks to an existing network.

FAQ

Q: Can the 1769-SDN act as a DeviceNet slave?

No. The 1769-SDN is a master/scanner only. For slave (adapter) functionality on a 1769 system a different module is required.

Q: How many 1769-SDN modules can one CompactLogix system have?

Multiple scanners can coexist on the same 1769 bus, each managing an independent DeviceNet network. The practical limit is the controller's I/O slot capacity and backplane current budget.

Q: Does the scanner need to be configured before the controller program is downloaded?

Yes. The scan list (configured in RSNetWorx) must be uploaded to the scanner module before it will communicate with slave nodes. The controller program and scanner configuration are independent — both must be in place for the system to function.

Q: What happens if a slave node goes offline during operation?

The scanner detects the absence of the expected node and sets a fault bit in its status data. Whether the controller program faults or continues depends on how the program handles that status bit — it's up to the application logic to decide.

Q: Can I commission the network with some nodes missing from the scan list?

Yes. Nodes not included in the scan list are ignored by the scanner. This allows staged commissioning — bring up critical nodes first, add others as they become available.

1769-SDN New Factory Sealed 1769SDN Ser B CompactLogix DeviceNet Scanner Module