2024年4月6日发(作者：封易巧)
Selectable I/O Standards in CycloneII Devices
Figure10–g a Cyclone II Device with a 5.0-Volt Device
5.0 V Device
Cyclone II Device
3.0 - 3.4 V ± 0.25 V
5.0 V ± 0.25 V
V
CC
V
CCIO
PCI Clamp
V
CCIO
I
R
2
Model as R
1
I
B
If V
CCIO
is between 3.0 V and 3.6 V and the PCI clamping diode is enabled,
the voltage at point B in Figure10–21 is 4.3 V or less. To limit large current
draw from the 5.0-V device, R
2
should be small enough for a fast signal
rise time and large enough so that it does not violate the high-level output
current (I
OH
) specifications of the devices driving the trace. The PCI
clamping diode in the Cyclone II device can support 25mA of current.
To compute the required value of R
2
, first calculate the model of the
pull-up transistors on the 5.0-V device. This output resistor (R
1
) can be
modeled by dividing the 5.0-V device supply voltage (V
CC
) by the
I
OH
:R
1
=V
CC
/I
OH
.
Figure10–22 shows an example of typical output drive characteristics of
a 5.0-V device.
Cyclone II Device Handbook, Volume 1
2024年4月6日发(作者：封易巧)
Selectable I/O Standards in CycloneII Devices
Figure10–g a Cyclone II Device with a 5.0-Volt Device
5.0 V Device
Cyclone II Device
3.0 - 3.4 V ± 0.25 V
5.0 V ± 0.25 V
V
CC
V
CCIO
PCI Clamp
V
CCIO
I
R
2
Model as R
1
I
B
If V
CCIO
is between 3.0 V and 3.6 V and the PCI clamping diode is enabled,
the voltage at point B in Figure10–21 is 4.3 V or less. To limit large current
draw from the 5.0-V device, R
2
should be small enough for a fast signal
rise time and large enough so that it does not violate the high-level output
current (I
OH
) specifications of the devices driving the trace. The PCI
clamping diode in the Cyclone II device can support 25mA of current.
To compute the required value of R
2
, first calculate the model of the
pull-up transistors on the 5.0-V device. This output resistor (R
1
) can be
modeled by dividing the 5.0-V device supply voltage (V
CC
) by the
I
OH
:R
1
=V
CC
/I
OH
.
Figure10–22 shows an example of typical output drive characteristics of
a 5.0-V device.
Cyclone II Device Handbook, Volume 1