Turns a USB port into a serial UART so a host sees a virtual COM port and the board gets TXD/RXD plus modem control lines. It handles USB 2.0 full-speed and UART rates up to 2 Mbps, and integrates the oscillator, voltage regulator, and a configurable EEPROM for the USB descriptors, so the external parts are just decoupling. Four GPIO pins add status LEDs or control. A compact, self-contained alternative to the FT232 and CH340 for USB serial.

Pinout

Pin	Name	Type	Function
1	RI	input	Ring Indicator control input (active low). Modem-status handshake line.
2	GND	power_in	Ground reference. Must be tied to ground.
3	D+	bidirectional	USB D+ full-speed (12 Mbps) differential data line. Connect to the USB connector D+ pin.
4	D-	bidirectional	USB D- full-speed (12 Mbps) differential data line. Connect to the USB connector D- pin.
5	VIO	power_in	I/O supply voltage input. Sets digital I/O rail from 1.8 V up to VDD. Decouple to GND.
6	VDD	power_in	Digital core supply (3.0 to 3.6 V). Also the output of the on-chip 3.45 V voltage regulator when REGIN is driven from VBUS (self- or USB-powered). Decouple to GND.
7	REGIN	power_in	5 V regulator input (3.0 to 5.25 V). Input to the on-chip 3.45 V LDO whose output appears on VDD. Typically tied to VBUS.
8	VBUS	input	VBUS sense input. Connect to the VBUS signal of the USB connector so the device can detect bus attach (2.5 V threshold).
9	RST	bidirectional	Device reset (active low). Open-drain output of internal POR / VDD monitor; may also be driven low externally for at least 15 us to initiate a system reset.
10	NC	unconnected	No connect. Leave floating or tie to VIO.
11	GPIO.3	bidirectional	User-configurable digital I/O. Supply is VIO (1.8 V to VDD). May be left unconnected when unused.
12	GPIO.2	bidirectional	User-configurable digital I/O; optional RS-485 transceiver bus-control output (Section 7.2). Supply is VIO.
13	GPIO.1	bidirectional	User-configurable digital I/O; optional receive-toggle output (Section 7.1). Supply is VIO.
14	GPIO.0	bidirectional	User-configurable digital I/O; optional transmit-toggle output (Section 7.1). Supply is VIO.
15	SUSPEND	output	Active-low USB suspend indicator. Driven low while the CP2104 is in the USB Suspend state.
16	VPP	passive	OTP ROM programming supply pin. Connect a 4.7 uF capacitor between this pin and ground to support ROM programming via the USB interface. During programming VPP is 5.75 V to VIO+3.6 V.
17	SUSPEND	output	Active-high USB suspend indicator. Driven high while the CP2104 is in the USB Suspend state.
18	CTS	input	Clear-To-Send hardware flow-control input (active low). Modem handshake line.
19	RTS	output	Request-To-Send hardware flow-control output (active low). Modem handshake line.
20	RXD	input	Asynchronous UART receive data input. Data rates 300 bps to 2 Mbps; 5/6/7/8 data bits; 1/1.5/2 stop bits; odd/even/mark/space/no parity.
21	TXD	output	Asynchronous UART transmit data output. Data rates 300 bps to 2 Mbps; 5/6/7/8 data bits; 1/1.5/2 stop bits; odd/even/mark/space/no parity.
22	DSR	input	Data-Set-Ready modem control input (active low).
23	DTR	output	Data-Terminal-Ready modem control output (active low).
24	DCD	input	Data-Carrier-Detect modem control input (active low).

Key specifications

Parameter	Value
Type	USB-to-UART bridge
USB	USB 2.0 full-speed
UART data rate	300 bps to 2 Mbps
GPIO	4 configurable
Integrated	Oscillator, regulator, EEPROM
Supply	VBUS or self-powered (3.0-3.6 V core)
Package	QFN-24 (4x4 mm)

Ordering variants

Same part, different packaging or reel option.

CP2104-F03-GM (QFN-24)
CP2104-F03-GMR (QFN-24, tape & reel)

CAD (KiCad official)

Symbol: Interface_USB:CP2104 (KiCad official)
Footprint: Package_DFN_QFN:QFN-24-1EP_4x4mm_P0.5mm_EP2.6x2.6mm
3D model: QFN-24 (KiCad packages3D, STEP)

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

Datasheet: Silicon Labs datasheet (22 pp, sha256 9569257991f26467, retrieved 2026-08-17, tier: manufacturer)
Extractor: ds2sf (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.
CAD: KiCad official libraries (CC-BY-SA 4.0).

Datasheet PDF