EP2C8T144C8N Datasheet, PDF (309/470 Pages) Altera Corporation – Cyclone II Device Handbook, Volume 1

Selectable I/O Standards in Cyclone II Devices
I/O Driver Impedance Matching (R_S) and Series Termination (R_S)
Cyclone II devices support driver impedance matching to the impedance
of the transmission line, typically 25 or 50 Ω. When used with the output
drivers, on-chip termination (OCT) sets the output driver impedance to
25 or 50 Ω by choosing the driver strength. Once matching impedance is
selected, driver current can not be changed. Table 10–7 provides a list of
output standards that support impedance matching. All I/O banks and
I/O pins support impedance matching and series termination. Dedicated
configuration pins and JTAG pins do not support impedance matching or
series termination.
Table 10–7. Selectable I/O Drivers with Impedance Matching and Series
Termination
I/O Standard
3.3-V LVTTL/CMOS
2.5-V LVTTL/CMOS
1.8-V LVTTL/CMOS
SSTL-2 class I
SSTL-18 class I
Target R_S (Ω)
25 (1)
50 (1)
50 (1)
50 (1)
50 (1)
Note to Table 10–7:
(1) These RS values are nominal values. Actual impedance varies across process,
voltage, and temperature conditions. Tolerance is specified in the DC
Characteristics and Timing Specifications chapter in volume 1 of the Cyclone II
Handbook.
Pad Placement
and DC
Guidelines
f
This section provides pad placement guidelines for the programmable
I/O standards supported by Cyclone II devices and includes essential
information for designing systems using the devices’ selectable I/O
capabilities. This section also discusses the DC limitations and guidelines.
Quartus II software provides user controlled restriction relaxation
options for some placement constraints. When a default restriction is
relaxed by a user, the Quartus II fitter generates warnings.
For more information about how Quartus II software checks I/O
restrictions, refer to the I/O Management chapter in volume 2 of the
Quartus II Handbook.
Altera Corporation
February 2008
10–27
Cyclone II Device Handbook, Volume 1