Selectable I/O Standards in Stratix II and Stratix II GX Devices
Output Pins
When a voltage-referenced input or bidirectional pad does not exist in a
bank, the number of output pads that can be used in that bank depends
on the total number of available pads in that same bank. However, when
a voltage-referenced input exists, a design can use up to 20 output pads
per VREF pin in a bank.
Bidirectional Pins
Bidirectional pads must satisfy both input and output guidelines
simultaneously. The general formulas for input and output rules are
shown in Table 4–9.
Table 4–9. Bidirectional Pin Limitation Formulas
Rules
Formulas
Input
<Total number of bidirectional pins> + <Total number of VREF
input pins, if any> 40 per VREF pin
Output
<Total number of bidirectional pins> + <Total number of
output pins, if any> – <Total number of pins from smallest
OE group, if more than one OE groups> 20 per VREF pin
■
If the same output enable (OE) controls all the bidirectional pads
(bidirectional pads in the same OE group are driving in and out at the
same time) and there are no other outputs or voltage-referenced
inputs in the bank, then the voltage-referenced input is never active
at the same time as an output. Therefore, the output limitation rule
does not apply. However, since the bidirectional pads are linked to
the same OE, the bidirectional pads will all act as inputs at the same
time. Therefore, there is a limit of 40 input pads, as follows:
<Total number of bidirectional pins> + <Total number of VREF input pins>
40 per VREF pin
■
If any of the bidirectional pads are controlled by different OE and
there are no other outputs or voltage-referenced inputs in the bank,
then one group of bidirectional pads can be used as inputs and
another group is used as outputs. In such cases, the formula for the
output rule is simplified, as follows:
<Total number of bidirectional pins> – <Total number of pins from smallest
OE group> 20 per VREF pin
Altera Corporation
January 2008
4–37
Stratix II Device Handbook, Volume 2
ALTERA [ ALTERA CORPORATION ]
