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62 IEEE 1394 Fundamentals and Interface Overview Chapter 4
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 HP E8491A PC
to VXI Interconnect
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.
Figure 4-4. Cross-section of the IEEE 1394 Cable.
135
246
6.1 mm
power wires
shields
signal pair wires
connector
PIN #
COMMENT
1
cable power
2
cable ground
3/4
strobe on receive,
data on transmit
5/6
data on receive,
strobe on transmit