Protocol scope and method
The common header is interpreted as big-endian length, serial, message ID, platform center ID, three version bytes, encryption flag and key.
4 + 4 + 2 + 4 + 3 + 1 + 4 = 22 header bytes.
Common questions
Does the JT/T 809 Header Decoder leave my browser?
No application upload is used. Avoid putting sensitive production data in shareable URLs.
Is this a standards compliance test?
No. Confirm the edition and vendor profile with licensed documents and your target platform.
Offline diagnostic aid. Verify fields, version and vendor extensions before production use.