User guide

FireWire

STINGRAY Technical Manual V4.4.4

FireWire connection capabilities

FireWire can connect together up to 63 peripherals in an acyclic network

structure (hubs). It allows peer-to-peer device communication (between dig-

ital cameras), to take place without using system memory or the CPU.

But even more importantly, a FireWire camera can directly, via direct mem-

ory access (DMA), write into or read from the memory of the computer with

almost no CPU load.

FireWire also supports multiple hosts per bus. FireWire requires only a cable

with the correct number of pins on either end (normally 6 or 9).

Capabilities of 1394a (FireWire 400)

FireWire 400 (S400) is able to transfer data between devices at 100, 200 or

400 MBit/s data rates. Although USB 2.0 claims to be capable of higher

speeds (480 Mbit/s), FireWire is, in practice, not slower than USB 2.0.

The 1394a capabilities in detail:

• 400 Mbit/s

• Hot-pluggable devices

• Peer-to-peer communications

• Direct Memory Access (DMA) to host memory

• Guaranteed bandwidth

• Multiple devices (up to 45 W) powered via FireWire bus

IIDC V1.3 camera control standards

IIDC V1.3 released a set of camera control standards via 1394a which estab-

lished a common communications protocol on which most current FireWire

cameras are based.

In addition to common standards shared across manufacturers, a special

Format_7 mode also provided a means by which a manufacturer could offer

special features (smart features), such as:

•higher resolutions

• higher frame rates

•diverse color modes

as extensions (advanced registers) to the prescribed common set.

Caution



While supplying such an amount of bus power is clearly a

beneficial feature, it is very important not to exceed the

inrush current of 18 mJoule in 3 ms.

Higher inrush current may damage the Phy chip of the

camera and/or the Phy chip in your PC.