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RocketIO™ Transceiver User Guide
UG024 (v3.0) February 22, 2007
Chapter 2:
Digital Design Considerations
R
Clock Ratio
USRCLK2 clocks the data buffers. The ability to send/receive parallel data to/from the
transceiver at three different widths requires the user to change the frequency of
USRCLK2. This creates a frequency ratio between USRCLK and USRCLK2. The falling
edges of the clocks must align.
shows the ratios for each of the three data widths.
Digital Clock Manager (DCM) Examples
With at least three different clocking schemes possible on the transceiver, a DCM is the best
way to create these schemes.
shows typical DCM connections for several transceiver clocks. REFCLK is the
input reference clock for the DCM. The other clocks are generated by the DCM. The DCM
establishes a desired phase relationship between TXUSRCLK, TXUSRCLK2, etc. in the
FPGA core and REFCLK at the pad.
NOTE:
The reference clock may be any of the four MGT clocks, including the BREFCLKs.
FF672
B14/C14
C13/B13
AD14/AE14
AE13/AD13
FF896
F16/G16
G15/F15
AH16/AJ16
AJ15/AH15
FF1152
H18/J18
J17/H17
AK18/AL18
AL17/AK17
FF1148
N/A
N/A
N/A
N/A
FF1517
E20/D20
J20/K20
AR20/AT20
AL20/AK20
FF1704
G22/F22
F21/G21
AU22/AT22
AT21/AU21
FF1696
N/A
N/A
N/A
N/A
Table 2-3:
BREFCLK Pin Numbers
Package
Top
Bottom
BREFCLK
Pin Number
BREFCLK2
Pin Number
BREFCLK
Pin Number
BREFCLK2
Pin Number
Table 2-4:
Data Width Clock Ratios
Data Width
Frequency Ratio of USRCLK\USRCLK2
1 byte
1:2
(1)
2 byte
1:1
4 byte
2:1
(1)
Notes:
1. Each edge of the slower clock must align with the falling edge of the faster clock.
Product Not Recommended for New Designs