FireWire Bandwidth Issues:

You can use the Firewire interface to get real time images onto the computer - provided that you do not violate the bandwidth of the 1394 bus.

 

While the 1394a bus is capable of 400 Mbps throughput that is for burst rates.

The Sustained Bandwidth of the 1394a bus is 256 Mbps.

 

While the 1394b bus is capable of 800 Mbps throughput that is for burst rates.

The Sustained Bandwidth of the 1394b bus is 512 Mbps.

 

You can choose your resolution, bit depth (8 to 24) and frame rate and as long as you are under 256 Mbps (or 512 Mbps for 1394b) you can get these images to the computer in real-time.

 

If you are using multiple cameras on the same PC you need to understand the following:

 

1) A single 1394 bus has the limitations mentioned above and if you put more than one camera onto this bus you must share the available bandwidth with the multiple cameras. You can program the cameras to share the bandwidth equally or you can program the cameras to have a set fixed bandwidth each but the total of all cameras must not violate the 256Mbps (or 512 Mbps for 1394b) limit for the single bus.

 

2) One way to get around this limitation is to add another 1394 bus to the PC by adding another 1394 card. This card will be a separate 1394 bus with the same limitations above. The beauty is the each 1394 card or bus can achieve the full bandwidth for that card. Thus if you need two cameras to have full bandwidth you can place each camera onto its own 1394 card (bus) and each will have 256Mps of bandwidth (or 512 Mbps for 1394b).

 

3) There are suppliers who offer 1394 cards that have individual multiple busses on them. These tend to be more expensive than simply using additional cards. These cards are usually over $250 each whereas you can purchase single cards for $10(NewEgg). But this option is nice if you do not have many available slots in the PC.

 

4) ISG offers on-board in-camera JPEG compression options for some cameras.  The JPEG compression can help with these bandwidth issues by compressing the image data prior to transmission.