XVME-212 Manual
August, 1989
2.7 MECHANICAL SWITCH/RELAY OPERATION
2.7.1
XVME-212/l
With the XVME-212/l, an isolated 12V DC supply is available for use with mechanical
switches. The 12V supply’s positive terminal is connected to the “+” terminal of each
input channel. The 12V supply’s return terminal is connected to pins 49 and 50 of the JK
connectors (see Table 2-9). The external switch should be connected between the “-”
terminal of the particular input channel and pins 49, 50. When the switch closes, the 12V
return is connected to the "-" terminal of the input channel which turns the input channel
on. No external supplies are required.
Note that all input channels have their “+" terminals connected together (they are all
connected to the 12V supply). Some users will want electrical isolation between channels.
To facilitate this, break points are available for all 32 input channels. When the
breakpoint is cut, the input channel’s “+" terminal is disconnected from the isolated
supply and the other input channels. The 12V supply cannot be used on a channel when
its break point is cut, however. These break points are labeled as CHO - CH31 on the
board and are easily accessible from the circuit side of the board under the 32 1 W
resistors. Pads are provided on either side of the break point to allow reconnection, if
required. The 300V channel-to-channel isolation specification applies onlv to channels
which have their break point cut. The 300V channel to VMEbus isolation is maintained
whether the break points are cut or not (because the 12V supply is isolated to 300V).
2.7.2
XVME-212/2
With the XVME-212/2, the +5V supply of the VME backplane is used with the mechanical
switches. Each “+" terminal of the input channels is connected to +5V (with reference to
logic ground) while pins 49 and 50 of the JK ports are connected to logic ground. (See
Table 2-9.) The external switch should be connected between the “-” terminal of the
particular input channel and pins 49, 50.
When the switch closes, logic ground is
connected to the “-" terminal of the input channel, which then turns on the input channel.
Note that all input channels have their “+” terminals connected together; they are all
connected to +5V.
Some users will want electrical isolation between channels. To
facilitate this, break points are available for all 32 input channels. When the breakpoint
is cut, the input channel’s “+" terminal is disconnected from the +5V supply and the other
input channels.
The +5V cannot
however.
These break points are
accessible from the circuit side of
break point to allow reconnection,
300V channel-to-VMEbus isolation
point cut.
be used on a channel once its break point is cut,
labeled CHO - CH31 on the board and are easily
the board. Pads are provided on either side of the
if required. The 300V channel-to-channel and the
applies ONLY to channels which have their break
2-13
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