KM Box Serial Control Solution

KM Box is built on CH645W. It receives text commands over a USB virtual serial port (115200 8N1) and presents a USB HID keyboard/mouse to the controlled PC. A physical keyboard/mouse can also pass through and switch between two hosts. A controller app or script sends km.* commands; the controlled side needs no special drivers.

Materials, hardware, and support

See CH645 / CH645W for IC specs. Design materials, hardware purchasing, and support are available via doc.ultrasemi.com. Treat firmware km.help() as the authoritative command list.

1. CH645W On-Chip Path vs Multi-Chip Stacks

Many KM / KVM builds combine an external USB HUB + MCU + analog USB switch (plus other bridges). Protocol traffic crosses board traces and chip-to-chip links repeatedly, so latency and jitter stack up—cursor drift, slow hotkeys, and weaker hot-plug behavior are common pain points.

This design uses one CH645W with multiple USB HS PHYs, composite/HUB channels, and KVM-oriented switching:

• Shorter on-chip communication: serial parsing, HID report generation, and dual-host KM switching stay inside the die—faster and more predictable than multi-chip board interconnects.
• Fewer companion ICs: no need to stack a HUB IC plus analog switch matrix just for KM routing—cleaner BOM and layout.
• Plug-and-play on the controlled PC: standard USB HID, no proprietary driver.
• Simple control protocol: 115200 8N1 text commands for move, click, keys, and strings.

IC specs, part comparison, and block diagram: CH645 page.

2. Product and Connection

Typical wiring:

Role	Connection	Notes
Controller	Script / host app sends text commands to the box serial port	USB virtual COM 115200 8N1
Controlled PC	USB to the box; OS sees a HID keyboard/mouse	Driver-free USB HID
Physical KM (optional)	Plug into the box USB ports	Shares cursor / focus with serial commands; dual-host switch

Controller PC                 Controlled PC
   │                              │
   │  USB virtual COM               │  USB HID KM
   │  115200 8N1                    │
   └──────────► KM Box (CH645W) ◄────┘
                  ▲
                  │ optional physical mouse / keyboard

Typical use cases: dual-PC office workflows, bring-up and test benches, industrial operator stations, and air-gapped control where the controller drives the target via HID without an extra network path.

3. Serial Parameters

Item	Value
Interface	USB virtual serial (COM port in Device Manager)
Baud rate	115200
Data bits	8
Parity	None
Stop bits	1
Line ending	End each command with a newline (Enter)

Notes:

• Keep each command under 64 characters when possible.
• Sending too fast may drop new commands when the internal queue is full—add spacing.
• Use a UTF-8 terminal so help text is not corrupted.

To list commands after connect, send km.help(). The device returns the supported command set and formats.

4. Command Syntax

• Commands start with km.; arguments go in parentheses.
• Separate multiple arguments with commas.
• Numbers may be negative, e.g. km.move(-50, 20).
• Keys may be names or numeric keycodes; strings use double quotes, e.g. km.string("Hello").
• Command names are case-insensitive (prefer lowercase).

5. Command Overview

Command	Function
km.help()	Show command list
km.init()	Clear keyboard state and release held keys
km.move(x,y)	Relative mouse move
km.left(x)	Left button down / up
km.right(x)	Right button down / up
km.middle(x)	Middle button down / up
km.side1(x)	Side button 1 (forward) down / up
km.side2(x)	Side button 2 (back) down / up
km.click(x,y)	Single mouse click
km.wheel(x)	Scroll wheel
km.turbo(x,y)	Auto-repeat mouse clicks
km.down(x)	Key down
km.up(x)	Key up
km.press(x,y)	Key tap (auto release)
km.string("text",t)	Type a string

6. Mouse Commands

6.1 Relative move km.move(x, y)

Arg	Meaning
x	Horizontal delta; right positive, left negative
y	Vertical delta; down positive, up negative (optional; omit for horizontal-only)

km.move(100)
km.move(100, 50)
km.move(-200, -80)

• Large distances are split into multi-step straight moves automatically.
• There is a per-command step limit; split very large moves.
• Motion is asynchronous—wait tens to hundreds of milliseconds before the next command.

6.2 Hold / release

km.left / km.right / km.middle / km.side1 / km.side2: 1 = down, 0 = up.

km.left(1)
km.left(0)
km.right(1)
km.side1(0)

These do not auto-release; send 0 yourself, or use km.click.

6.3 Single click km.click(x, y)

Arg	Meaning
x	1 left, 2 right, 3 middle, 4 side1, 5 side2
y	Hold time in ms; default 75; optional

km.click(1, 50)
km.click(2, 100)

6.4 Wheel km.wheel(x)

Positive scrolls up; negative scrolls down. Examples: km.wheel(3), km.wheel(-5).

6.5 Turbo km.turbo(x, y)

Arg	Meaning
x	1–5 per table; 0 disables all turbo
y	Interval in ms; 0 disables that button; omit ≈ 100ms

x	Button
1	Left
2	Right
3	Middle
4	Side 1
5	Side 2

km.turbo(1, 80)
km.turbo(1, 0)
km.turbo(0)

7. Keyboard Commands

7.1 Key notation

• Names (preferred): km.down("a"), km.press("enter"), km.press("1")
• Numeric keycodes: km.down(4) (see HID keyboard scan codes)
• A single quoted uppercase letter implies Shift: km.press("A")

7.2 Down / up / press

km.down("w")
km.up("w")
km.press("a")
km.press("enter", 100)

km.press(x, y) presses then releases; y is hold time in ms (default 75).

7.3 Type string km.string("text", t)

Types ASCII in order, with Shift handling for uppercase and common symbols. t is per-character delay in ms (default 75).

km.string("Hello")
km.string("Hi", 100)

7.4 Reset km.init()

Stops text input, clears keyboard state, and releases serial-held keys. Use after script faults or stuck keys.

8. Common Key Names

Category	Examples
Letters / digits	a–z, 0–9
Editing	enter, esc, backspace, tab, space, capslock
Modifiers	shift / lshift, ctrl / lctrl, alt / lalt, win / lgui
Navigation	up down left right, home end, pageup/pgup, pagedown/pgdn
Function	f1–f12, insert/ins, delete/del, printscreen

Ask support or validate on hardware for the full name list.

9. Examples

9.1 Move then left-click

km.move(300, 200)

After motion settles (typically 200–500 ms depending on distance):

km.click(1, 75)

9.2 Chord Ctrl+C

km.down("ctrl")
km.press("c", 50)
km.up("ctrl")

9.3 Type text and Enter

km.string("notepad")
km.press("enter", 80)

9.4 Left-button turbo and stop

km.turbo(1, 50)
km.turbo(0)

Or: km.turbo(1, 0).

9.5 Recovery

km.init()
km.left(0)
km.right(0)

10. Troubleshooting

Symptom	Suggestion
No response	Check COM port, baud 115200, and trailing newline
Occasional drops	Slow the send rate; keep commands ≤ 64 chars
Choppy long moves	Large moves are multi-step by design
Stuck keys	Run km.init() and km.up for held keys
Mouse button stuck	Send km.left(0) (etc.) or replug USB
No absolute screen coordinates	Relative move only; compute offsets on the controller
Separate controller / controlled PCs	Cursor position cannot be read back; coordinate with software on the controlled side or stay relative

11. Notes

• MCU: CH645W.
• Authoritative command set: device km.help() output.
• This page tracks user manual v1.0.