[Electronic Keying] If the compatibility bit is set in the forward open message, the connection is refused although the requested revision is lower than the target revision

If the compatibility bit is set in the forward open message, the connection is refused although the requested revision is lower than the stack's own revision.

Example 1:

• Target has revision 2.3
• PLC sends ForwardOpen including an electronic key with compatibility bit set to 1 and revision set to 1.2

==> This forward open is rejected by the stack although the requested revision is "older" than the actual revision of the device.

Example 2:

• Target has revision 2.3
• PLC sends ForwardOpen including an electronic key with compatibility bit set to 1 and revision set to 1.4

==> This forward open is accepted.

If the major revisions match, the stack accepts only minor revisions that are higher than the stack's own minor revision. ==> Not OK

Solution:

• Requested major revision is greater than stack's major revision ==> reject
• Requested major revision equals the stack's major revision
  • if requested minor revision is lower or equal the stack's minor revision ==> accept
  • otherwise ==> reject
• Requested major revision is lower than stack's major revision ==> accept