If I upgrade my DECS-400 to a DECS-450 Controller, is my existing IDP-800 or IDP-801 still compatible?

The IDP-800-B was originally designed to operate with the DECS-400 digital excitation controller. Communication between the IDP-800-B and the DECS-400 uses the Modbus protocol in one of two ways:

- Modbus RTU over an RS-485 serial link, or

- Modbus TCP over an Ethernet network.

The IDP-801-B was developed as a direct, drop-in replacement for the IDP-800-B when used with the DECS-400. Functionally, it serves the same role, but there are hardware differences between the IDP-800 and IDP-801. These differences are documented in the IDP-801 instruction manual for review.

When upgrading from a DECS-400 to a DECS-450, Basler provides a Legacy Modbus Map in the DECS-450. This feature allows you to continue using your existing DECS-400 register map so you do not need to immediately reconfigure all Modbus-based devices. Because of this legacy map, an existing IDP-800-B or IDP-801-B can still communicate with a DECS-450 using the same register structure that was used with the DECS-400.

However, there are several important considerations when using an IDP-800-B or IDP-801-B with a DECS-450:

1. **Security Settings and Reset Function**

The DECS-450 implements a different security structure than the DECS-400. For the IDP to be able to issue a Reset command successfully over Modbus, the Modbus port’s “Unsecured Access” level in the DECS-450 must be set to “Settings.”

- If this is not configured, the Reset and potentially other commands from the IDP will not function as expected.

- This setting is part of the DECS-450’s approach to controlling which functions can be performed without higher security authorization.

2. **Change from Dedicated to Programmable Inputs**

The DECS-450 replaces some of the “dedicated” input functions found in the DECS-400 with “programmable” inputs. This improves flexibility but also affects bit assignments in the input status registers as seen over Modbus.

- As a result, the input status bits that the IDP-800-B/IDP-801-B expects for specific functions may no longer align directly with the same physical inputs on the DECS-450.

- This behavior is best understood by comparing the input bit definitions for the DECS-400 and DECS-450.

For example, consider Modbus register 40204:

To illustrate the impact of this change, assume the DECS-400 uses “Input 3” to represent Breaker Status. In the DECS-400, this is reported as register 40204, bit 8 (SW3). When moving to the DECS-450, register 40204, bit 8 is now labeled “Input 7” (IN7), not “Input 3.”

This means that a device such as the IDP-800-B/IDP-801-B, which expects Breaker Status at a particular bit position, may now be reading a different logical input unless the mapping and logic are reviewed and adjusted.

** IDP-801-E **

The IDP-801-E was created specifically for use with the DECS-450. When you use an IDP-801-E with a DECS-450, the same security and input offset considerations described above still apply.

In the field, the IDP-801-B can be upgraded to an IDP-801-E by loading a file supplied by Basler Electric. This is a firmware update that adapts the IDP-801 for DECS-450 applications. The IDP-800-B cannot be upgraded in this way due to memory limitations in its original hardware design.

It is important to note that this upgrade does not change the underlying Modbus communication behavior; it primarily updates the user-facing wording on the IDP-801 so that it references the DECS-450 instead of the DECS-400, helping operators clearly identify which controller the IDP is intended to support.

** IDP-1201 **

Basler Electric does offer an IDP-1201 which is fully compatible with the DECS-450, taking advantage of newer features.  However, because this is a larger 12-inch display (compared to the 8-inch unit), retrofitting it into existing IDP-800/801 installations may be challenging.

https://www.basler.com/resource-hub/manuals/instruction-manual/idp-801-instruction-manual-rev-g-english/9437600991.pdf