EP4CE30F29C7N Datasheet, PDF (110/488 Pages) Altera Corporation – Cyclone IV Device Handbook, Volume 1

6–4
Chapter 6: I/O Features in Cyclone IV Devices
I/O Element Features
Table 6–2 on page 6–7 shows the possible settings for I/O standards with current
strength control. These programmable current strength settings are a valuable tool in
helping decrease the effects of simultaneously switching outputs (SSO) in conjunction
with reducing system noise. The supported settings ensure that the device driver
meets the specifications for IOH and IOL of the corresponding I/O standard.
1 When you use programmable current strength, on-chip series termination (R_S OCT) is
not available.
Slew Rate Control
The output buffer for each Cyclone IV I/O pin provides optional programmable
output slew-rate control. Table 6–2 on page 6–7 shows the possible slew rate option
and the Quartus II default slew rate setting. However, these fast transitions may
introduce noise transients in the system. A slower slew rate reduces system noise, but
adds a nominal delay to rising and falling edges. Because each I/O pin has an
individual slew-rate control, you can specify the slew rate on a pin-by-pin basis. The
slew-rate control affects both the rising and falling edges. Slew rate control is available
for single-ended I/O standards with current strength of 8 mA or higher.
1 You cannot use the programmable slew rate feature when using OCT with calibration.
1 You cannot use the programmable slew rate feature when using the 3.0-V PCI,
3.0-V PCI-X, 3.3-V LVTTL, or 3.3-V LVCMOS I/O standards. Only the fast slew rate
(default) setting is available.
Open-Drain Output
Cyclone IV devices provide an optional open-drain (equivalent to an open-collector)
output for each I/O pin. This open-drain output enables the device to provide
system-level control signals (for example, interrupt and write enable signals) that are
asserted by multiple devices in your system.
Bus Hold
Each Cyclone IV device user I/O pin provides an optional bus-hold feature. The
bus-hold circuitry holds the signal on an I/O pin at its last-driven state. Because 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 necessary to hold a signal
level when the bus is tri-stated.
The bus-hold circuitry also pulls undriven pins away from the input threshold
voltage in which 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.
1 If you enable the bus-hold feature, the device cannot use the programmable pull-up
option. Disable the bus-hold feature when the I/O pin is configured for differential
signals. Bus-hold circuitry is not available on dedicated clock pins.
Bus-hold circuitry is only active after configuration. When going into user mode, the
bus-hold circuit captures the value on the pin present at the end of configuration.
Cyclone IV Device Handbook,
Volume 1
May 2013 Altera Corporation