USB-C Pinout Explained What Do CC1 and CC2 Pins Do?
- 1. USB-C CC Pins: The Two Wires That Run the Show
- 2. How CC1 and CC2 Detect Attach and Orientation
- 3. Rp, Rd, and Current Advertisement
- 4. USB Power Delivery Rides on the CC Line
- 5. Accessory and Audio Modes Detected Through CC
- 6. Design Implications for the CC Pins
- 7. Bench Debugging of the CC Pins: Failure Symptoms and Measurements
- 8. Frequently Asked Questions (FAQ)
USB-C CC Pins: The Two Wires That Run the Show
The USB-C CC pins — CC1 and CC2, located on positions A5 and B5 of the connector — are the intelligence channel of every USB Type-C link. While the power and high-speed lanes move the payload, CC1 and CC2 detect whether anything is attached, establish the direction of the connection, advertise how much current the source can deliver, carry USB Power Delivery messages, and power active cables. Understanding the USB-C pinout therefore means understanding these two pins first.
The reason there are two CC pins is the flippable connector. A full-featured USB-C cable contains only one CC wire, and the cable's internal wiring determines which of the two receptacle pins it lands on. When you plug in the connector one way, the far side sees activity on CC1; flip it, and the signal moves to CC2. Orientation detection is simply the receiver noticing which pin carries the signal.
| Pin Group | Positions | Function |
|---|---|---|
| VBUS | A4, A9, B4, B9 | Power rail (5 V default, up to 48 V with PD) |
| GND | A1, A12, B1, B12 | Ground return |
| CC1 / CC2 | A5 / B5 | Configuration Channel: attach detect, orientation, power advertise, PD |
| SBU1 / SBU2 | A8 / B8 | Sideband use (DisplayPort AUX, audio) |
| TX/RX pairs | A2/A3, A10/A11, B2/B3, B10/B11 | SuperSpeed differential lanes |
| D+/D− | A6/A7, B6/B7 | USB 2.0 data (both sides wired in cable) |
How CC1 and CC2 Detect Attach and Orientation
A USB-C source (DFP) presents a pull-up resistor Rp on both CC pins; a sink (UFP) presents a pull-down Rd (5.1 kΩ) on both CC pins. With nothing connected, both CC lines at the source sit at their Rp-determined voltage. When a cable is plugged in, exactly one of the source's CC lines sees its voltage divider change because that line now reaches a sink's Rd through the cable's single CC wire. The other CC line stays open — or carries VCONN when the cable is active.
This one-wire arrangement elegantly solves three problems at once: attachment (a divider changed state), orientation (which pin changed tells you the flip state), and current advertisement (the Rp value encodes the default current capability before any PD negotiation). The USB-C CC1 CC2 pair is, in effect, a two-pin state machine.
Rp, Rd, and Current Advertisement
Before Power Delivery negotiation even starts, the resistor values set the baseline power contract. The source selects one of three Rp pull-up values — presenting default USB current, 1.5 A, or 3.0 A — and the sink reads the resulting CC voltage to know how much current it may draw without any digital communication. A dead-battery phone can safely draw charge moments after plug-in because this analog contract needs no firmware.
| Rp Pull-Up (to 5 V) | Advertised Current | Typical Source |
|---|---|---|
| 56 kΩ | Default USB (500 mA / 900 mA) | Legacy hosts, hubs |
| 22 kΩ | 1.5 A | Chargers, powered hubs |
| 10 kΩ | 3.0 A | Full-size chargers, docks |
Note the asymmetry of roles: sources pull up, sinks pull down. A port that must act as both (a DRP, dual-role port) switches between Rp and Rd repeatedly until a partner locks on. If you are designing a sink, remember that omitting or mis-valuing Rd is a classic reason a device fails to charge from a compliant source.
USB Power Delivery Rides on the CC Line
USB PD communication uses the same CC wire that just did attach detection, using BMC (biphase mark coding) signaling at the CC pin. All PD messages — voltage requests, current limits, data role swaps, and the higher-power contracts up to 240 W (48 V / 5 A) under PD 3.1 EPR — travel over this single wire in half-duplex. That is why CC trace layout deserves the same care as a clock line: keep it short, route it away from the SuperSpeed pairs, and place the PD controller close to the connector.
The other CC pin is not idle during PD communication. In systems with powered or active cables, the source supplies VCONN (traditionally around 5 V, limited current) on the CC pin that is not carrying the communication — powering the electronMarked cable's chip that reports its capabilities. VCONN is why active Thunderbolt and 5 A-rated cables cost more: there is a chip inside drinking from that line.
Accessory and Audio Modes Detected Through CC
CC pins also carry the accessory vocabulary. A simple analog headset adapter presents Ra (approximately 1 kΩ) on both CC pins, which tells the phone to enter Audio Accessory Mode and route analog audio to the SBU pins. Debug accessories announce themselves with different CC combinations. These modes matter to connector selection because they assume the receptacle's CC pins reach your controller — a hard-wired Rp-only design loses them.
Design Implications for the CC Pins
- Place the CC/PD controller as close to the receptacle as practical; the CC trace is a communication line, not a static net.
- Provide ESD protection on CC1 and CC2 — they are exposed to every plug-in event and to charged cables.
- Never tie CC1 and CC2 together; that defeats orientation detection and can confuse PD negotiation.
- For sink designs, fit 5.1 kΩ Rd pull-downs on both CC pins (or use a controller that integrates them).
- For designs that use active cables, budget a VCONN switch and current limit on the unused CC pin.
For the connector itself — pin-count variants, mounting styles, and mid-mount options — see our USB-C connector types overview and the Ultimate Guide to USB Type-C connectors. If you are deciding between 16-pin and 24-pin parts, the trade-off analysis in our connector types article covers which applications can drop the SuperSpeed lanes and which cannot.
Bench Debugging of the CC Pins: Failure Symptoms and Measurements
Most USB-C attach problems come down to the CC pins, and they show up on the bench in recognizable patterns. A device that does nothing at all when a cable is plugged in usually has both CC pins floating or a missing 5.1 kOhm Rd resistor on a sink. A device that only works in one orientation has a single-sided CC failure: one of CC1 or CC2 is open, so attach is only detected when the cable is flipped to the working line. A device that negotiates 5 V but never reaches higher voltages usually has an issue in the PD communication layer that rides on the same CC line rather than in the physical attach logic.
The first measurement on a failing board is DC voltage on both CC pins at the connector, one orientation at a time. On a sink facing a 3 A source advertisement, the pulled-up CC line reads roughly 0.85 to 1.2 V depending on Rp value, while the unused CC line should show no pull-up activity. Compare CC1 and CC2 readings across both cable orientations; a healthy design shows mirror-image behavior. A line that reads 5 V means the pull-up is being driven straight from VBUS and something is miswired; a line that reads 0 V on both orientations with a known-good source suggests an open solder joint on that contact.
- Always test with both a passive cable and an e-marked active cable; active cables can mask or mimic CC faults
- Measure with the cable flipped and label readings by orientation, not by time, to keep the data usable
- Check the 5.1 kOhm Rd resistors with power off: wrong value or wrong placement is the single most common build error
- Scope the CC line during PD negotiation: the BMC bursts are small-signal on top of the DC level and reveal whether negotiation even starts
One habit worth adopting from module-level debug: keep a known-good breakout board with accessible CC test points on every bench. Probing a populated connector directly risks shorting adjacent pins with the probe tip, and the small contact pitch turns a measurement into a damage event. The breakout board pays for itself the first time it distinguishes a broken cable from a broken design in under a minute.
