Stratix Architecture
I/O pin has an individual slew-rate control, allowing you to specify the
slew rate on a pin-by-pin basis. The slew-rate control affects both the
rising and falling edges.
Bus Hold
Each Stratix device I/O pin provides an optional bus-hold feature. The
bus-hold circuitry can weakly hold the signal on an I/O pin at its last-
driven state. Since the bus-hold feature holds the last-driven state of the
pin until the next input signal is present, an external pull-up or pull-down
resistor is not needed to hold a signal level when the bus is tri-stated.
shows bus hold support for different pin types.
Table 2–29. Bus Hold Support
Pin Type
I/O pins
Bus Hold
v
CLK[15..0]
CLK[0,1,2,3,8,9,10,11]
FCLK
FPLL[7..10]CLK
v
The bus-hold circuitry also pulls undriven pins away from the input
threshold voltage where noise can cause unintended high-frequency
switching. You can select this feature individually for each I/O pin. The
bus-hold output drives no higher than V
CCIO
to prevent overdriving
signals. If the bus-hold feature is enabled, the programmable pull-up
option cannot be used. Disable the bus-hold feature when using open-
drain outputs with the GTL+ I/O standard or when the I/O pin has been
configured for differential signals.
The bus-hold circuitry uses a resistor with a nominal resistance (R
BH
) of
approximately 7 kΩ to weakly pull the signal level to the last-driven state.
See the
DC & Switching Characteristics
chapter of the
Stratix Device
Handbook, Volume 1
for the specific sustaining current driven through this
resistor and overdrive current used to identify the next-driven input
level. This information is provided for each V
CCIO
voltage level.
The bus-hold circuitry is active only after configuration. When going into
user mode, the bus-hold circuit captures the value on the pin present at
the end of configuration.
Altera Corporation
July 2005
2–121
Stratix Device Handbook, Volume 1
ALTERA [ ALTERA CORPORATION ]
