Altera Cyclone IV, Device Handbook

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Chapter 5: Clock Networks and PLLs in Cyclone IV Devices 5–23
Clock Feedback Modes
October 2012 Altera Corporation Cyclone IV Device Handbook,
Volume 1
Clock Feedback Modes
Cyclone IV PLLs support up to five different clock feedback modes. Each mode
allows clock multiplication and division, phase shifting, and programmable duty
cycle. For the supported feedback modes, refer to
Table 5–5 on page 5–18 for
Cyclone IV GX PLLs and Table 5–6 on page 5–19 for Cyclone IV E PLLs.
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Input and output delays are fully compensated by the PLL only if you are using the
dedicated clock input pins associated with a given PLL as the clock sources.
When driving the PLL using the GCLK network, the input and output delays may not
be fully compensated in the Quartus II software.
Source-Synchronous Mode
If the data and clock arrive at the same time at the input pins, the phase relationship
between the data and clock remains the same at the data and clock ports of any I/O
element input register.
Figure 5–12 shows an example waveform of the data and clock in this mode. Use this
mode for source-synchronous data transfers. Data and clock signals at the I/O
element experience similar buffer delays as long as the same I/O standard is used.
Source-synchronous mode compensates for delay of the clock network used,
including any difference in the delay between the following two paths:
■ Data pin to I/O element register input
■ Clock input pin to the PLL phase frequency detector (PFD) input
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Set the input pin to the register delay chain in the I/O element to zero in the
Quartus II software for all data pins clocked by a source-synchronous mode PLL.
Also, all data pins must use the
PLL COMPENSATED logic option in the Quartus II
software.
Figure 5–12. Phase Relationship Between Data and Clock in Source - Synchronous Mode
Data pin
PLL reference
clock at inp u t pin
Data at register
Clock at register