When a DL06 project needs more than four interrupt points, adding networked PLCs does not make a remote input behave like a local interrupt. First identify which signals need genuinely immediate action; keep each hard-response input and its controlled output on the same PLC, then select a controller architecture that provides the required local interrupt capacity.
Measure the required response before changing the hardware
List each input, the output or action it must trigger, and the maximum acceptable input-to-output delay. Separate actions that must happen immediately from supervisory work that can tolerate a longer delay. This distinction decides whether an interrupt resource is necessary and whether a networked, multi-PLC arrangement is acceptable.
Measure the existing response at the machine under representative operating conditions. Record the input event and the resulting output transition with an appropriate capture method, and compare the worst observed delay with the process limit. Do not treat a stated PLC scan time as the complete response time: the scan-bound portion depends on when the input changes relative to program execution, and a remote action also includes communication and processing delays.
If a few milliseconds meets the process requirement, investigate ordinary or immediate input handling before purchasing more interrupt hardware. If the process requires microsecond response, evaluate whether a PLC is the right device for that function; a PLC may need to supervise a faster device rather than provide the fastest control action itself.
Check the DL06 interrupt limit and the required instruction path
The DL06 configuration described here has four usable interrupt points. If all four are already assigned, treating ordinary ladder logic as an equivalent interrupt does not create another fast-response point. Regular OUT coils remain scan-time bound.
Interrupt-driven logic only delivers its intended response when the relevant action is implemented in the interrupt routine with interrupt-compatible instructions. The documented discussion specifically identifies OUTI, SETI, and RSTI; it warns that a regular OUT remains subject to scan timing. Check the actual routine and output instruction before concluding that the interrupt function is working.
| Reading or observation | Meaning | Next check |
|---|---|---|
| Four interrupt points are assigned on the DL06 | The stated DL06 interrupt capacity is exhausted. | Check whether the controller can be changed to a supported interrupt-card arrangement, or divide fast functions among local controllers. |
| An interrupt occurs but the output response is scan-bound | The action may be using a regular output instruction or may be performed outside the interrupt routine. | Review the interrupt routine and instruction path; verify the actual output action uses the interrupt mechanism. |
| The action works locally but is delayed across PLCs | Networked processing adds communication and PLC scan delays. | Keep the time-critical input-to-output pair local, or confirm measured remote latency meets the process limit. |
Check whether a DL260 and D2-CTRINT solve the capacity problem
For the 260 CPU, the stated interrupt option is the D2-CTRINT card. It still provides only four interrupt points, and the described arrangement does not allow more than one CTRINT card. Therefore, this option does not solve a requirement for more than four interrupt points on that CPU by stacking additional cards.
Use this branch when four local interrupt sources are sufficient and the controller/card arrangement fits the application. If the requirement remains sixteen distinct interrupt responses, proceed to the distributed-control or higher-capacity-system decision; do not count a second card as available capacity.
Reject networked interrupts for actions that must happen now
Transferring interrupt information between PLCs adds latency. The response path includes the receiving PLC's scan, the communication-channel delay, and the other PLC's scan. Ethernet or serial communications may suit slower supervisory data, but they do not preserve the immediacy of a local interrupt.
A project used four DL06 PLCs linked with Ethernet cards to provide sixteen interrupt response points. Treat that as a distributed architecture, not as a method for making one DL06 expose sixteen local interrupts. Validate every time-critical path independently; if an input on one PLC must immediately operate an output, place that input and output on that same PLC.
Assign each fast input and output to one local controller
A tiered system can work when each interrupt input is assigned to a PLC that controls the specific output requiring the fast response. Keep the low-level, interrupt-based reaction in that PLC. Transfer non-interrupt, higher-level information between controllers using the available data-sharing method, such as RX/WX; use serial or Ethernet via ECOM when slower shared data needs to move between PLCs.
This arrangement has a hard boundary: a remote PLC cannot perform the local interrupt action for an input it does not own. Any later supervisory decision that crosses the network follows the networked delay path. Before splitting logic, map every input-to-output dependency and flag any signal that must cross a PLC boundary.
- Group the inputs by the output or action each one must trigger.
- Assign every hard-response input and its controlled output to the same PLC.
- Keep the fast action in that PLC's interrupt routine and use interrupt-capable instructions where required.
- Transfer only the slower, non-interrupt information to the main or supervisory PLC using the selected data-sharing link.
- Measure the full response path for any action that crosses controllers; reject the split if it exceeds the process limit.
Compare the 16-point architecture before committing to a replacement
The described higher-capacity option is a DL405 8-point interrupt module, with two such modules in a 450 system providing sixteen interrupt points. This is an alternative to distributing the points across four DL06 PLCs and network cards, not an expansion card stated for the DL06 or the 260 CPU.
Compare the complete system cost and required response behavior, not just the interrupt module count. Confirm the applicable CPU and module configuration from current manufacturer documentation before ordering; the system option described here is specific to the DL405/450 arrangement. If choosing multiple DL06 controllers, account for the communication path and the requirement to colocate each fast input/output pair.
Restore local response and verify every interrupt path
Temporary restore: If production needs to resume before a hardware redesign, move only those functions whose response time allows it to scan-based or supervisory logic, or use a spare suitable controller to host a complete local input-to-output interrupt path. Do not label a networked reaction as an immediate interrupt. Record which actions have a changed response class and operate only within the process limits.
Permanent repair: Select the supported local interrupt capacity or allocate fast functions across multiple controllers. Keep hard-response pairs local, implement the response in the interrupt routine, and use network transfers only for slower data.
- Confirm the assigned interrupt input and its controlled output are on the same PLC.
- Inspect the interrupt routine and verify the response uses the required interrupt instruction path rather than a regular scan-bound
OUT. - Trigger each input individually and confirm the intended output changes.
- Measure input-to-output delay for each local path and compare it with the required process limit.
- For every networked supervisory function, measure end-to-end delay separately and confirm that it is acceptable for that slower task.
- Document the point assignment, controller ownership, and any action intentionally left scan- or network-bound.
Stop the change if the required response is microsecond-scale, if an output must be controlled remotely with hard timing, or if the selected CPU/module configuration is unclear. Confirm the architecture with current AutomationDirect documentation or official AutomationDirect support before commissioning.
Frequently asked questions about DL06 interrupt points
What happens if all four DL06 interrupt points are already used?
The stated DL06 capacity is four interrupt points, so additional hard-response inputs need another architecture. Check the 260 with a D2-CTRINT for a four-point option, distribute local fast functions across PLCs, or evaluate the stated DL405/450 alternative for sixteen points.
What happens if I add a second D2-CTRINT card?
The described 260 arrangement allows only one D2-CTRINT, and that card provides four interrupt points. Do not plan capacity around installing a second CTRINT.
What happens if I send an interrupt input over Ethernet to another PLC?
The remote response adds communication delay and PLC scan time, so it is not equivalent to a local interrupt. Keep the immediate input/output action on one PLC and use Ethernet or serial communication for supervisory data only when its measured delay is acceptable.
What happens if I need 16 interrupt points?
The described alternatives are four DL06 PLCs with Ethernet links, assigning each fast input and its output locally, or a DL405/450 system with two 8-point interrupt modules. Stop before purchase or commissioning if timing requirements or hardware compatibility remain unclear, and confirm the design with current AutomationDirect documentation or official support.