Information Technology Reference
In-Depth Information
Slot 0
Slot 5
P2 has
2
×
12 lines
P3 has
2
×
24 lines
Slot 1
Slot 2
Slot 3
Slot 4
Figure 22.7
Local bus backplane
22.4.5 Analogue SUMBUS
The Analogue SUMBUS provides for an analogue-summing node for all connected modules.
It is possible for each module to drive the summing line using an analogue current source.
Every module can also read from this line, using a high-impedance receiver. It is typically
used to generate a complex waveform, where one or more modules can each provide a part
of the waveform. For example, three modules could each provide a single frequency which
are then summated onto the SUMBUS.
22.4.6 Module identification bus
This bus provides for an identification of the connected modules. It uses 12 identification
wires which all connect to slot 0, and then one connection to each of the other slots. If a
module is plugged into a slot, then it provides a ground connection for the module identifica-
tion line, otherwise it will be an open circuit. This allows for quick system configuration at
start-up and aids in diagnostics. Typically the module in slot 0 will scan the bus when it is
started, if a module that is connected fails to communicate, the device in slot 0 may display
an error for that device.
22.4.7 Power bus
The power bus provides:
•
Up to 268 W for each module.
•
Voltages of
+
5
V,
+
12 V, -12 V and
+
5V standby (battery backup) from the VME bus.
•
Voltages of +24 V and -24 V for analogue circuits for the VXI bus.
•
ECL voltages of -5.2 V and -2 V for ECL.
