46
RocketIO™ Transceiver User Guide
UG024 (v3.0) February 22, 2007
Chapter 2:
Digital Design Considerations
R
.DSSEN
( 1'b0 ),
.PSCLK
( 1'b0 ),
.PSEN
( 1'b0 ),
.PSINCDEC
( 1'b0 ),
.RST
( 1'b0 ),
.CLK0
( clk_i ),
.CLK90
( ),
.CLK180
( ),
.CLK270
( ),
.CLK2X
( ),
.CLK2X180
( ),
.CLKDV
( ),
.CLKFX
( ),
.CLKFX180
( ),
.LOCKED
( DCM_LOCKED ),
.PSDONE
( ),
.STATUS
( )
);
BUFG buf1 (
.I
( clk_i ),
.O
( USRCLK_M )
);
IBUFG buf2(
.I ( REFCLKIN ),
.O ( REFCLKINBUF )
);
endmodule
Example 1b: Two-Byte Clock without DCM
If TXDATA and RXDATA are not clocked off the FPGA using the respective USRCLK2s,
then the DCM may be removed from the two-byte clocking scheme, as shown in
Example 2: Four-Byte Clock
If a 4-byte or 1-byte data path is chosen, the ratio between USRCLK and USRCLK2
changes. The time it take for the SERDES to serialize the parallel data requires the change
in ratios.
The DCM example (
) is detailed for a 4-byte data path. If 3.125 Gb/s is required,
REFCLK is 156 MHz and USRCLK2_M runs at only 78 MHz, including the clocking for
Figure 2-3:
Two-Byte Clock without DCM
MGT for 2-Byte Data Path (no DCM)
GT_std_2
REFCLKSEL
REFCLK
TXUSRCLK2
RXUSRCLK2
TXUSRCLK
RXUSRCLK
0
REFCLK_P
IBUFGDS BUFG
REFCLK_N
ug024_02b_062404
Note:
Implementation tools automatically
instantiate the BUFG. There is no need to
explicitly instantiate in HDL code.
Product Not Recommended for New Designs