Clock Ratio; Digital Clock Manager (Dcm) Examples; Table 3-7: Data Width Clock Ratios; Table 3-8: Dcm Outputs For Different Data_Widths - Xilinx RocketIO User Manual

Clocking
Table 3-6: Clock Ports (Continued)
Clock I/Os
TXUSRCLK2 Input
Notes:
1. Will be available in ISE 5.1.

Clock Ratio

USRCLK2 clocks the data buffers. The ability to send parallel data to 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. Finally, for a 4-byte data path, the 1-byte data path creates a clocking scheme where
USRCLK2 is phase-shifted 180° and at twice the rate of USRCLK.

Table 3-7: Data Width Clock Ratios

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.
Table 3-8
input reference clock for the DCM. The other clocks are generated by the DCM. The DCM
establishes a desired phase relationship between RXUSRCLK, TXUSRCLK, etc. in the
FPGA core and REFCLK at the pad.

Table 3-8: DCM Outputs for Different DATA_WIDTHs

TX_DATA_WIDTH
SERDES_10B
RX_DATA_WIDTH
FALSE
FALSE
FALSE
TRUE
TRUE
TRUE
Notes:
1. Since CLK0 is needed for feedback, it can be used instead of CLK180 to clock USRCLK or USRCLK2 of the transceiver with
the use of the transceiver's local inverter, saving a global buffer (BUFG).
UG024 (v1.5) October 16, 2002
RocketIO™ Transceiver User Guide
Clock from FPGA used to clock TX data and status between the transceiver and FPGA
fabric. The relationship between TXUSRCLK2 and TXUSRCLK depends on the width
of the transmission data path.
Data Width
1 byte
2 byte
4 byte
Notes:
1. Each edge of slower clock must align with falling edge of faster clock
shows typical DCM connections for several transceiver clocks. REFCLK is the
REFCLK
1
2
4
1
2
4
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Description
Frequency Ratio of USRCLK\USRCLK2
TXUSRCLK
RXUSRCLK
CLKIN CLK0
CLKIN CLK0
CLKIN CLK180
CLKIN CLKDV (divide by 2)
CLKIN CLKDV (divide by 2)
CLKIN CLKFX180 (divide by 2)
1-800-255-7778
(1)
1:2
1:1
(1)
2:1
TXUSRCLK2
RXUSRCLK2
CLK2X180
CLK0
(1)
CLKDV (divide by 2)
CLK180
CLKDV (divide by 2)
CLKDV (divide by 4)
R
(1)
39