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INTERFACE.md

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K85 RGB Control Interface

Because the K85 only supports a single color for all keys and no interesting effect, this is a much shorter interface description than for the MasterKeys keyboards.

USB Interface

bVendor: 0x1044 Chu Yuen Enterprise Co., Ltd
bProduct: 0x7a14

iManufacturer: Texas Instruments
iProduct: MSP430-USB Example

Configurations: 1
Interfaces: 4 (!)

As you can see in the above code block, the keyboard reports its manufacturer to be Texas Instruments, and its product to be an Example. This is a great example of lazy manufacturers.

It appears there is only an ANSI variant of this keyboard, and thus there probably aren't any other bProduct ids around.

Hardware details

The keyboard is indeed powered by a MSP430 MCU produced by Texas Instruments and for which there a great Reference Design, but it appears that Gigabyte (or the OEM that built this keyboard for them?) did not move past implementing the RGB functionality and releasing the software.

Without an actual teardown of the keyboard it is impossible to tell how the LEDs are really controlled, but my best guess is that the through-hole mounted RGB LEDs have a common anode and split cathodes and that all all these LEDs are in parallel. The cathodes of each of the colours is then probably connected to the drain of an N-channel MOSFET that is controlled using PWM from the MCU.

Even if the LEDs were 5050 SMD LEDs or some similar design, the MCU would probably not be able to control all the LEDs independently and provide <1ms response times, in case you were wondering.

Interfaces and Endpoints

The the USB descriptor reports not one, not two, but four interfaces.

# Interface 0: HID Keyboard
Just a plain keyboard interface
EndPoint 1  IN: 0x81, 8 bytes
EndPoint 1 OUT: 0x01, 8 bytes

# Interface 1: HID 64N Interface
Perhaps the firmware updating interface? No idea, really.
EndPoint 1  IN: 0x82, 20 bytes
EndPoint 1 OUT: 0x02: 20 bytes

# Interface 2: HID Mouse (!)
Yeah, this keyboard also has a mouse interface.
EndPoint 3  IN: 0x83, 8 bytes
EndPoint 3 OUT: 0x83, 8 bytes

# Interface 3: HID DataPipeline interface
RGB LED Control interface
EndPoint 4  IN: 0x84, 64 bytes
EndPoint 4 OUT: 0x04, 64 bytes

As indicated, only the last interface and endpoints are interesting here. They provide a really simple interface to controlling the RGB LEDs.

RGB Control Protocol

Set the color to rr, gg, bb in hex:

3f 08 01 c8 rr gg bb 08 01 00 ..

3f 08 01 09 01 ** 01 01 08 00 ..

The ** indicate the brightness parameter. The RGB color can be brightness-scaled using the brightness (ranging from 0x00 to 0x05). Do yourself a favour and don't use that option anywhere but just adjust your RGB tuple.

There are two effects available on the K85, probably also sporting additional parameters set in the second packet, but they are too boring and can easily be implemented in software. I have not decoded the protocol for adjusting that.

Practical implications

Just send the second listed packet once, and then simply adjust the color of the LEDs by only sending the first packet with different RGB color values. The second packet is not needed to adjust the color of the LEDs (the first packet probably prompts for a registry write immediately, the color remains after power cycling the keyboard).