What is the difference between ISOBUS VT Version 3 and Version 4?

VIRTEC display.
VIRTEC display.

The ISO 11783-6 standard was most recently released in 2010. As of this release, three common versions of the Virtual Terminal (VT) are specified. These versions are referenced in the standard as “Version 2”, “Version 3”, and “Version 4”. Based on recent ISOBUS Plugfest attendance, a survey of the industry shows a few Version 2 devices still in common use, a small number of Version 4 devices in use, and a large majority of devices using Version 3. The standard requires that an Electronic Control Unit (ECU) and a VT communicating via the VT standard should use the standard according to the lowest VT version of the pair, e.g. a VT at Version 4 and an ECU at Version 3 should use Version 3 communications.

In a discussion regarding a new VT design, we strongly recommend against using VT Version 2. The differences between VT Version 2 and VT Version 3 are only significant in one key area: Aux Control. The Aux Type 2 is defined for Version 3 and later and is not compatible with Aux Type 1 in Version 2 and prior. Aux Type 1 and Aux Type 2 are incompatible, so we recommend making the choice to use Aux Type 2.

Differences between VT Version 3 and VT Version 4 can be broken down into 4 categories:
1. Clarifications and incremental improvements;
2. Modifications to requirements;
3. New optional features; and
4. New required features.

For a full list of these differences, read more here: https://www.distek.com/about/isobus-vt/