PATH ADC Home > Documentation > Hardware
> Power Mac G4 Developer Note
|
The FireWire connector has six contacts, as shown in Figure 3-2 . The connector signals and pin assignments are shown in Table 2 .
Figure 3-2 FireWire connector
The power pin provides up to 15 W total power on both connectors. The voltage on the power pin is unregulated, ranging from 20 V under a typical load to 30 V under no load. The power pin also accepts external power at 8 to 33 V, in conformity with the 1394 standard, to keep the FireWire bus connected when the computer is turned off.
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.