Selectable I/O Standards in Cyclone II Devices
VREF Pad Placement Guidelines
To maintain an acceptable noise level on the VCCIO supply and to prevent
output switching noise from shifting the VREF rail, there are restrictions on
the placement of single-ended voltage referenced I/Os with respect to
VREF pads and VCCIOand ground pairs. Use the following guidelines for
placing single-ended pads in Cyclone II devices.
The Quartus II software automatically does all the calculations in this
section.
Input Pads
Each VREF pad supports up to 15 input pads on each side of the VREF pad
for FineLine BGA devices. Each VREF pad supports up to 10 input pads on
each side of the VREF pad for quad flat pack (QFP) devices. This is
irrespective of VCCIOand ground pairs, and is guaranteed by the
Cyclone II architecture.
Output Pads
When a voltage referenced input or bidirectional pad does not exist in a
bank, there is no limit to the number of output pads that can be
implemented in that bank. When a voltage referenced input exists, each
VCCIOand ground pair supports 9 output pins for Fineline BGA
packages (not more than 9 output pins per 12 consecutive row I/O pins)
or 5 output pins for QFP packages (not more than 5 output pins per 12
consecutive row I/O pins or 8 consecutive column I/O pins). Any
non-SSTL and non-HSTL output can be no closer than two pads away
from a VREF pad. Altera recommends that any SSTL or HSTL output,
except for pintable defined DQ and DQS outputs, to be no closer than two
pads away from a VREF pad to maintain acceptable noise levels.
1
Quartus II software will not check for the SSTL and HSTL
output pads placement rule.
Refer to “DDR and QDR Pads” on page 10–32 for details about guidelines
for DQ and DQS pads placement.
Bidirectional Pads
Bidirectional pads must satisfy input and output guidelines
simultaneously.
Refer to “DDR and QDR Pads” on page 10–32 for details about guidelines
for DQ and DQS pads placement.
Altera Corporation
February 2008
10–29
Cyclone II Device Handbook, Volume 1
ALTERA [ ALTERA CORPORATION ]
