ISOBUS VT

Differences between ISOBUS VT Version 3 and Version 4

Introduction

The ISO11783-6 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 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.

Differences between VT Version 3 and VT Version 4

1. Clarifications or incremental improvements

We recommend all the differences in this section be implemented according to the VT Version 4 standard regardless of the version being implemented.

  1. Text justification is defined as being on a pixel (graphical) basis in VT Version 4 (see section 4.6.16.1).
  2. Usage of the CR, LF, BS, and 0x00 characters are precisely defined in VT Version 4 (4.6.16.5).
  3. VT Version 4 must support the Execute Macro command (Annex Table A.1).
  4. VT Version 4 must reserve 16 object types (numbered 240-255) for proprietary objects (Annex Table A.1).
  5. A Soft Key pointer to the Null Object ID is explicitly required to reserve an empty spot in the Soft Key Mask in VT Version 4 (Annex B.5).
  6. The Select Input Object command is supported for Key objects and Button objects in VT Version 4 (Annex B.6, B.7).
  7. The Enable/Disable Object command is supported for Button objects in VT Version 4 (Annex B.7).
  8. The options byte for the Button object has an associated AID and can be read or written with the Change Attribute command in VT Version 4 (Annex Table B.14).
  9. A Boolean Input value of anything other than 0 is defined as True for VT Version 4 (Annex B.8.2).
  10. Truncation of decimal values is explicitly controlled by an option bit in VT Version 4 (Annex Tables B.18 and B.23).
  11. VT Version 4 has clarified the minimum, maximum, target, and value parameters of Output graphic objects – Meter, Linear Bar Graph, and Arched Bar Graph (Annex B.11.1).
  12. The VT Version 4 Get Hardware response indicates if the hardware:  supports simultaneous activation of all Physical Soft Keys; supports simultaneous activation of all Buttons; reports the Drag event via the Pointing Event message; or supports intermediate coordinates during the Drag event (Annex D.9).
  13. The number of physical Soft Keys used for navigating Virtual Soft Keys is reported in the Get Number of Soft Keys response message in VT Version 4 (Annex D.5).
  14. The maximum number of seconds from power cycle to transmission of the first VT Status message is reported in the Get Hardware response in VT Version 4 (Annex D.9).
  15. The number of physical Soft Keys used for navigating Virtual Soft Keys is reported in the Get Number of Soft Keys response message in VT Version 4 (Annex D.5).
  16. The maximum number of seconds from power cycle to transmission of the first VT Status message is reported in the Get Hardware response in VT Version 4 (Annex D.9).
  17. The Load Version response has additional diagnostic information in the Acknowledgement field in VT Version 4 (Annex E.7).

2. Modifications to requirements

We recommend against implementing the VT Version 4 changes in this section unless Version 4 VT is being developed.

  1. The number of virtual Soft Keys should be exactly 64 in VT Version 4 but could be any value from 6 to 64 in prior versions (4.5.2.c).
  2. The Input String and Output String objects are defined differently between VT Version 4 and prior versions (Annex Tables B.17 and B.23).
  3. The Memory Required field of the Get Memory message also includes the estimated size of all Graphics Context objects in VT Version 4 (Annex D.2).

3. New optional features

Version 3 devices on the market may make use of some of these features if they are implemented, so a business case for implementing any of these could be made even if a Version 3 VT is being developed.

  1. VT Version 4 may support proportional font sizes (4.6.16.3).
  2. VT Version 4 may support displaying data from multiple working sets using the Window Mask and Key Group objects (4.7).  Note that VT Version 4 is required to parse these objects even if it does not support use of them.
  3. VT Version 4 may support the following objects:  Window Mask, Key Group, Graphics Context, Color Map, and Object Label Reference List (Annex Table A.1), but is required to parse all of them in an object pool.

4. New required features

Version 3 devices on the market may make use of some of these features if they are implemented, so a business case for implementing any of these could be made even if a Version 3 VT is being developed.

  1. VT Version 4 must have at least 6 physical soft keys, whereas prior versions had no minimum requirement (4.5.2.a).  Note that “Physical Soft Keys” does not strictly imply physical membrane buttons; it is common practice for this to mean dedicated touchscreen locations.
  2. VT Version 4 must send the Audio Signal Termination message (4.6.11).
  3. VT Version 4 must support Font Tables as listed in Annex L.3 – L.7 including the first Unicode page (4.6.16.6, Annex L).
  4. VT Version 4 must support Output List and Extended Input Attributes objects (Annex Table A.1).
  5. Additional options were added to the Button object for Suppress Border, Transparent Background, Disabled, and No Border in VT Version 4 (Annex Table B.14).
  6. Input and Output Strings and Numbers support vertical text justification in VT Version 4 (Annex Tables B.17, B.18, B.22, B.23).
  7. Input and Output Strings support wrapping on the hyphen character (0x2D) in VT Version 4 (Annex Tables B.18 and B.22).
  8. Input Numbers and Input Lists support Real-Time data input (transmitting the value to the ECU as it is being changed) in VT Version 4 (Annex Tables B.18 and B.20).
  9. The VT Version 4 Get Hardware response indicates if the hardware:  supports simultaneous activation of all Physical Soft Keys; supports simultaneous activation of all Buttons; reports the Drag event via the Pointing Event message; or supports intermediate coordinates during the Drag event (Annex D.9).
  10. The Select Input Object response indicates if an object is opened for Edit in VT Version 4 (Annex F.7).
  11. The Select Input Object response indicates an error code for an Invalid Option value in VT Version 4 (Annex F.7).
  12. The Soft Key Activation message indicates if a key press is aborted in VT Version 4 (Annex H.2).
  13. The Button Activation message indicates if a button press is aborted in VT Version 4 (Annex H.4).
  14. Using the Select Input Object command, VT Version 4 supports activating a data input object (numeric or string) rather than just setting focus to the object (Annex F.6).
  15. For the Pointing Event message, VT Version 4 adds the Touch States for Released and Held in addition to the Touch State Pressed which was defined in prior versions (Annex H.6 and H.7).
  16. For the VT Select Input Object message, VT Version 4 adds a flag to indicate an object is open for data input (Annex H.8).

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