Octagon XE-900, Reference Manual

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74
Chapter 11: PC/104 and PC/104-Plus expansion
Description
The PC/104 and PC/104 -Plus connectors allow you to interface expansion modules
such as A/D converters, CardBus, digital I/O, serial ports, etc. Modules can be
stacked to form a highly integrated control system. The PC/104
-Plus expansion bus
supports mastering devices.
Note The actual maximum number of modules in a stack is limited primarily to the
capacitive loading on the bus and the electrical noise environment. This is
especially true when wide temperature operation is required. Good design practice
dictates that the modules present only one load to each bus signal. Unfortunately,
there are modules on the market that violate this practice by loading the bus more
heavily. Typically, it is the IOW*, IOR*, MEMW*, and RSTDRV* lines. For
example, if the IOW* line is routed to four ICs on the module without a buffer, then
the loading is equivalent to four PC/104 modules. Stacks with three or more
expansion modules should be carefully tested under all environmental conditions.
If possible, query the manufacture of the expansion module regarding loading. All
Octagon products present one load.
The situation is even more critical for the PC/104- Plus connector since the bus
speed is four times faster. The PC/104 -Plus connector and the PC/104 -Plus module
represent one load each. Adding more than one PC/104 -Plus module (two loads)
should trigger the same testing as discussed in the previous paragraph.
–
12V PC/104 -Plus devices
The XE–900 does not provide
–
12V to the PC/104 -Plus connector. If your PC/104 -
Plus board requires
–
12V, you must power it from a source other than the PC/104 -
Plus connector. If your power supply provides
–
12V, then you can power your
PC/104 -Plus card from J8 pin 9. READ THE FOLLOWING CAUTION BEFORE
INSTALLING YOUR CARD.
CAUTION
On the XE–900 PC/104 -Plus J3 connector, the
–
12V pin (A30) is tied to
ground (see table on page 110). If you do use a
–
12V PC/104 -Plus card and
provide external power, you must clip pin A30 on your PC/104 -Plus card
before you connect it to the XE–900. Otherwise, the
–
12V will be shorted to
ground and you will destroy your cards.