B.6.2.2 MODID LINES
The MODID lines allow a logical device to be identified with a particular physical location or slot. These lines
are sourced from the VXIbus Slot 0 module to the Slot 1 and higher modules. There is one line to each
module, located on P2 pin A30. A total of 12 MODID lines will connect between Slot 0 and the other modules
in a maximally configured VXIbus subsystem. In addition to these 12 lines, Slot 0 has its own MODID line
(MODID00). The purpose of the MODID lines is to:
1. Detect the presence of a module in a slot, even if that module has failed.
2. Identify the geographical location (slot number) of a particular device.
3. Indicate by lamp or other means the actual physical location of the module.
Slot 0 detects the presence of a module by the module pulling down its MODID line with a fixed resistor to
ground. This allows any module, even if failed and unpowered, to be detected.
The slot number of a device is identified by the Slot 0 module asserting a particular MODID line, and polling
the MODID bit in each module's A16 configuration space to detect the selected device.
A visual indicator, such as a lamp, may be placed adjacent to a slot (or even on the module) to illuminate when
that particular MODID line is driven true. This may be used to quickly identify the location of any module,
including failed modules. Refer to Figure B.1 for rules for loading and driving the MODID lines.
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