HP E8491A The HP E8491A PC to VXI Interconnect

shields
signal pair wires		connector
		1	3	5
		2	4	6
6.1 mm	PIN #		COMMENT
	1		cable power
	2		cable ground
	3/4	strobe on receive,
			data on transmit
	5/6		data on receive,
		strobe on transmit
power wires

Figure 4-4. Cross-section of the IEEE 1394 Cable.

The HP E8491A PC to VXI Interconnect

The power wires route power from the host adapter to devices (nodes) on the bus, whether the devices are turned on or off. Since each device in the system acts as a repeater, the power supplied to a device that is turned off enables signals to be transferred across that device. This maintains signal continuity throughout the system.

The E8491A is a VXI C-size device (Figure 4-5) normally installed in mainframe slot 0. With a logical address of 0, the E8491A functions as the mainframe’s resource manager via software included with the I_O libraries. The E8491A has 128 kBytes of shared RAM and contains many of the clock and triggering features found on the HP E1406A Command Module - a VXI resource manager/slot 0 device common in many GPIB-based systems. A VXI mainframe with the HP E8491A in slot 0 can also be powered on/off at any time without affecting other mainframes in the system.

The HP E8491A IEEE 1394 interconnect links the VXI backplane to the IEEE 1394 bus. However, the E8491A and the IEEE 1394 bus do not extend the (VXI) backplane between frames in multi-frame VXI systems. This means that the multimeter and multiplexers in a VXI scanning multimeter for example, must be installed in the same mainframe. Devices sharing the VXI Local bus must also be installed in the same mainframe.

62 IEEE 1394 Fundamentals and Interface Overview Chapter 4