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March 13th, 2021 08:00
U3821DW, unexpected values for VCP Code 60
I got a new monitor (DELL U3821DW) and am using a tool to switch input sources from the command line. My 2 old Dell monitors always worked fine with this tool and returned the standard value 0x0F when using the DisplayPort and 0x11 when using the HDMI 1 input port.
The U3821DW returns however for VCP Code 60 (Input Select) the value 3855 (0xF0F) when using DisplayPort 1. And when using the Input source HDMI 1 the value used is displayed as 4369 (0x1111).
I only changed the monitor, all other components: video-card, OS, etc. are the same.
The specifications (VESA Monitor Control Command Set Standard Version 2.2a) shows that VCP Code 60 is a single byte value and the other 3 bytes should always be set to 0.
Is this a known issue of this monitor type or has the second byte a special meaning?
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swamped207
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March 13th, 2021 12:00
The VESA MCCS is so old now that it simply cannot handle the new features new monitors have. You want to use only the low byte when reading and writing the active input, and you should be ok with your tool.
U3821DW-user
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March 20th, 2021 09:00
Thanks for the tip, reading and writing only the lower bytes works fine. The VESA MCCS standard may already exist for a long term, it is fuzzy. Why the U3821DW doesn't set these upper bytes to zero, as all the older Dell model do?