Last Revision Date: 5/1/2014
This article describes issues that users should be aware of when using IEEE-1394a digital cameras with IEEE-1394b OHCI cards.
1394b is a significant enhancement to the basic 1394 specification that enables speed increases to 800 Megabits/sec, supports distances of 100 meters on UTP-5, plastic optical fiber and glass optical fiber, and significantly reduces latency times by using arbitration pipelining. It is fully backwards compatible with the current 1394-1995 and 1394a specifications.
All of our 1394a cameras will work seamlessly with a 1394b host adapter. The issues that users should be aware of are:
- Unlike USB and USB 2.0, the physical interface between 1394a and 1394b is significantly different. As such, users will need to acquire cables with a 1394a (4-pin or 6-pin) connector on one end and a 1394b (9-pin) connector on the other.
- Connecting a 1394a device to a 1394b bus limits the bandwidth of the bus to 400 Megabits/sec. Therefore, it is not possible to run two 1394a devices at full speed on a 1394b bus.
- Using a 1394b Host Controller card will not improve the camera's ability to transmit data. That is, users will not be able to achieve higher resolutions and faster frame rates with their 1394a camera.
- It is unclear if the latency associated with getting incoming data to main memory will be decreased with 64bit/66MHz 1394b cards.
- There may be some issues if the 1394b network contains mixed devices. Although it will be transparent to 1394a devices, some 1394b devices may suffer issues when mixed with 1394a devices on the same network.