Syntax: setvcp <display-selection-options> (feature-code) [+|-] new-value) *
In full generality, the new-value argument to setvcp is a 2 byte number. A handful of monitors have continuous features with values greater than 255. Also, the settable VCP feature x73 (Gamma) has a complex 2 byte encoding. Other than these exceptional casess, all settable values are integer values in the range 0..255, i.e. a single byte.
Values can be specified either in decimal form, or as 1 or 2 byte hex numbers, with a leadning 'x'. Examples:
$ ddcutil setvcp 10 50 $ ddcutil setvcp 10 0x32 $ ddcutil sdtvcp 73 x5304
Multiple feature/new-value pairs can be given on a single setvcp command. For example:
$ ddcutil setvcp 10 50 12 75
It is possible to specify a relative instead of absolute value for a continuous feature by putting " + " or " - " between the feature id and value.
- The plus or minus signs must surrounded by spaces to indicate a relative value operation.
- The new value is adjusted so that it is never less than 0 or greater than the maximum value of the feature.
- In this situation setvcp first reads the current value before writing the adjusted value.
For example, to adjust the brightness value up or down by 5:
$ ddcutil setvcp 10 + 5 $ ddcutil setvcp 10 - 5
When ddcutil sends a Set VCP Feature packet to a display, it receives an acknowlegement at the I2C level that the request packet was received. The is no acknowledgement that the display has successfully executed the command. There have been occasional reports that the setvcp command appeared to succeed, but the new value was not set.
Therefore setvcp (and loadvcp) by default perform a getvcp operation to verify that the new value has actually been set. (Obviously, this verification does not occur for write-only features. It also does not occur for features such as x60 (Input Source) for which verification can be expected to fail.)
For most monitors, this verification is unnecessary. To improve performance it is possible to skip value verification using the --noverify option.
Display informational messages regarding verification.
Parse the new value based on the the specified MCCS (aka VCP) version, instead of the version obtained from feature xDF (VCP Version).