6I68 Manual 3
HARDWARE CONFIGURATION
CONNECTOR POWER
The power connection on the I/O connectors pin 49 can supply either 3.3V or 5V
power. Supplied power should be limited to 400 mA per connector.
When the following jumpers are in the left position, 5V power is supplied to pin 49
of the associated connector. When the jumper is in the right position, 3.3V power is
supplied to to pin 49 of the associated connector.
W12 selects the voltage supplied to P2. (I/O connector for bits 0..23)
W13 selects the voltage supplied to P3. (I/O connector for bits 24..47)
W14 selects the voltage supplied to P4. (I/O connector for bits 48..71)
W3 selects the voltage supplied to P7. (I/O connector for bits 72..95)
W2 selects the voltage supplied to P6. (I/O connector for bits 96.119)
W1 selects the voltage supplied to P5. (I/O connector for bits 120..143)
BUS SWITCH MODE
The 6I68 uses bus switch devices in series with all I/O pins. These devices allow the
3X2X inputs to be 5V tolerant and allow the I/O pins to be pulled up to 5V. The bus switch
input protection function works by disconnecting the FPGA from the IO pins when the IO
pin voltage rises above a preset threshold. This threshold determines the bus switch
operational mode and is selectable for the three left hand I/O connectors and the three right
hand I/O connectors separately. We refer to the modes as 5V mode and 3.3V mode.
When in 5V mode, the inputs and tri-stated outputs may be pulled up to 5V. This
allows driving 5V referred loads such as I/O module racks. The disadvantage of 5V mode
is that the output impedance is higher in the high output state (when the FPGA pins are at
3.3V) as the bus switch is off when the FPGA pin is at 3.3V. When 3.3V mode is selected,
the bus switch is always fully on unless input voltages >4V are applied, at which point the
bus switch disconnects the FPGA from the I/O pin. 3.3V mode is suggested for general
use.
When the bus switch mode jumper is in the UP position, 5V mode is selected, when
DOWN, 3.3V bus switch mode is selected.
W6
Sets bus switch mode for P2,P3,P4, = IO 0..71
W11 Sets bus switch mode for P7,P6,P5 = IO 72..143
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