Using Multiple Cameras on a Single Bus and Managing BandwidthBasler scout 26311 Using Multiple Cameras on aSingle Bus and ManagingBandwidthThis section includes information about using multiple cameras on a single IEEE 1394 bus.11.1 Using Multiple Cameras Where AllDevices are 1394bMost of the information included in this manual assumes that you have a single camera attached toyour 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 handlemultiple devices (such as cameras) connected to a single bus. And the connected devices canshare 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 oncamera is transmitting an image at any given time. In this situation, the camera transmitting imagescan use 100% of the bus bandwidth. In many situations, however, you would like to have two (ormore) cameras transmitting images at the same time. In this case, the cameras that are transmittingimages 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 busarchitecture 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 analternative, the bus can carry several packets from different devices where the sum of the packetsizes is 8192 bytes or less. These two situations are illustrated in Figure 84.In situation 1 shown in the figure, a single camera (camera A) is attached to the bus and we wantthat camera to use 100% of the bandwidth available during each bus cycle. In this case, we wouldset 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 threecameras will transmit image data simultaneously. We want camera A to use 25%, of the availablebus bandwidth, camera B to use 25%, and camera 3 to use 50%. In this case, we would set cameraA 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 itsends. As shown in the figure, the bus carries the packets sequentially on each cycle. The total byteload in all of the packets combined is 8192 and is equal to the maximum allowed per cycle. Note
