Preliminary Information
Cyclone FPGA Family Data Sheet
A path in which a pin directly drives a register may require a
programmable delay to ensure zero hold time, whereas a path in which a
pin drives a register through combinatorial logic may not require the
delay. Programmable delays decrease input-pin-to-logic-array and IOE
input register delays. The Quartus II Compiler can program these delays
to automatically minimize setup time while providing a zero hold time.
Programmable delays can increase the register-to-pin delays for output
registers. Table 12 shows the programmable delays for Cyclone devices.
Table 12. Cyclone Programmable Delay Chain
Programmable Delays
Quartus II Logic Option
Input pin to logic array delay
Input pin to input register delay
Output pin delay
Decrease input delay to internal cells
Decrease input delay to input registers
Increase delay to output pin
There are two paths in the IOE for a combinatorial input to reach the logic
array. Each of the two paths can have a different delay. This allows the
designer to adjust delays from the pin to internal LE registers that reside
in two different areas of the device. The designer sets the two
combinatorial input delays by selecting different delays for two different
paths under the Decrease input delay to internal cells logic option in the
Quartus II software. When the input signal requires two different delays
for the combinatorial input, the input register in the IOE is no longer
available.
The IOE registers in Cyclone devices share the same source for clear or
preset. The designer can program preset or clear for each individual IOE.
The designer can also program the registers to power up high or low after
configuration is complete. If programmed to power up low, an
asynchronous clear can control the registers. If programmed to power up
high, an asynchronous preset can control the registers. This feature
prevents the inadvertent activation of another device’s active-low input
upon power up. If one register in an IOE uses a preset or clear signal then
all registers in the IOE must use that same signal if they require preset or
clear. Additionally a synchronous reset signal is available to the designer
for the IOE registers.
External RAM Interfacing
Cyclone devices support DDR SDRAM and FCRAM interfaces at up to
133 MHz through dedicated circuitry.
Altera Corporation
51
ALTERA [ ALTERA CORPORATION ]
