FireWire Connector

The FireWire connector has six pins, as shown in Figure 3-2. The connector signals and pin assignments are shown in Table 3-2.

Figure 3-2 FireWire connector

Table 3-2 Signals on the FireWire connector

Pin	Signal name	Description
1	Power	Approximately 25 V DC
2	Ground	Ground return for power and inner cable shield
3	TPB-	Twisted-pair B, differential signals
4	TPB+
5	TPA-	Twisted-pair A, differential signals
6	TPA+
Shell	—	Outer cable shield

The power pin provides up to 15 W total power on both connectors. The voltage on the power pin is approximately 25 V.

Pin 2 of the 6-pin FireWire connector is ground return for both power and the inner cable shield. In a FireWire cable with a 4-pin connector on the other end, such as the one included with the computer, the wire from pin 2 is connected to the shell of the 4-pin connector.

The signal pairs are crossed in the cable itself so that pins 5 and 6 at one end of the cable connect with pins 3 and 4 at the other end. When transmitting, pins 3 and 4 carry data and pins 5 and 6 carry clock; when receiving, the reverse is true.