Basler SCOUT LIGHT User Manual download pdf (Page 141)

Using Multiple Cameras on a Single Bus and Managing Bandwidth

Basler scout light 133

10 Using Multiple Cameras on a

Single Bus and Managing

Bandwidth

This section includes information about using multiple cameras on a single IEEE 1394 bus.

10.1 Using Multiple Cameras Where All

Devices are 1394b

Most of the information included in this manual assumes that you have a single camera attached to

your IEEE 1394b bus. But is it also quite common to attach more than one camera to a single bus.

One of the main advantages of the IEEE 1394 bus architecture is that it is designed to handle

multiple devices (such as cameras) connected to a single bus. And the connected devices can

share the available bandwidth on the bus.

One way you can manage two cameras on a single bus is to operate the cameras so that only on

camera is transmitting an image at any given time. In this situation, the camera transmitting images

can use 100% of the bus bandwidth. In many situations, however, you would like to have two (or

more) cameras transmitting images at the same time. In this case, the cameras that are transmitting

images simultaneously must share the available bus bandwidth.

To understand how bandwidth is shared on an IEEE 1394 bus, we need to look at a few bus

architecture basics. The IEEE 1394b bus operates on a 125 microsecond cycle. During each cycle,

the bus can carry a single packet from one device with a packet size up to 8192 bytes. As an

alternative, the bus can carry several packets from different devices where the sum of the packet

sizes is 8192 bytes or less. These two situations are illustrated in Figure 35.

In situation 1 shown in the figure, a single camera (camera A) is attached to the bus and we want

that camera to use 100% of the bandwidth available during each bus cycle. In this case, we would

set the camera so that it would put 8192 bytes into the packet that it sends on each cycle of the bus.

In situation 2, we have three cameras (cameras A, B, and C) attached to the bus and all three

cameras will transmit image data simultaneously. We want camera A to use 25%, of the available

bus bandwidth, camera B to use 25%, and camera 3 to use 50%. In this case, we would set camera

A so that it would put 2048 bytes, i.e., 25% of the 8192 byte maximum, into each packet it sends.

We would set camera B so that it would put 2048 bytes (25% of 8192) into each packet it sends.

And we would set camera C so that it would put 4096 bytes (50% of the 8192) into each packet it

sends. As shown in the figure, the bus carries the packets sequentially on each cycle. The total byte

load in all of the packets combined is 8192 and is equal to the maximum allowed per cycle. Note

1 2 ... 136 137 138 139 140 141 142 143 144 145 146 ... 165 166

No comments

Basler SCOUT LIGHT User Manual Page 141