Why can a DDC command work when reading its value fails?

DDC reads and writes are separate operations. A monitor can accept a command even when its reply is missing, malformed or unavailable through the connection. A failed read alone does not prove that the corresponding write cannot work.

Compare the same monitor and command through a direct connection and through the adapter or dock, where possible. A difference helps locate the problem, but does not by itself prove whether the adapter or the monitor’s handling of that input is responsible. Use a supported command and confirm the result on the monitor. Successful command submission alone is not a measurement of its state.

A raw DDC read returns a 16-bit value, from 0 to 65535. For example, decimal 4369 is hexadecimal 0x1111. The value contains 0x11 in both its high and low byte. If the expected input code is 0x11, such a result can reflect a malformed monitor reply. It does not mean the CLI printed the same number twice. Do not automatically discard the high byte for every command, because both bytes can be meaningful.

See DDC connection troubleshooting, reading hardware brightness and the CLI reference for supported queries and parameter meanings.