Xilinx 1000BASE-X manual Method

Ten-Bit-Interface Logic

R

Virtex-4 Devices

Method 1

The Virtex-4 FPGA logic used by the example design delivered with the core is illustrated in Figure 6-4. This shows a Virtex-4 device IDDR primitive used with the DDR_CLK_EDGE attribute set to SAME_EDGE (see the Virtex-4 FPGA User Guide). This uses local inversion of pma_rx_clk0 within the IOB logic to receive the rx_code_group[9:0] data bus on both the rising and falling edges of pma_rx_clk0. The SAME_EDGE attribute causes the IDDR to output both Q1 and Q2 data on the rising edge of pma_rx_clk0.

For this reason, pma_rx_clk0 can be routed to both pma_rx_clk0 and pma_rx_clk1 clock inputs of the core as illustrated.

Caution! This logic relies on pma_rx_clk0 and pma_rx_clk1 being exactly 180 degrees out of phase with each other since the falling edge of pma_rx_clk0 is used in place of pma_rx_clk1. See the data sheet for the attached SERDES to verify that this is the case.

The IDELAY elements can be adjusted to fine-tune the setup and hold times at the TBI IOB input flip-flops. The delay is applied to the IDELAY elements using constraints in the UCF; these can be edited if desired. See “Ten-Bit Interface Constraints” in Chapter 12 for more information.

component_name_block (Block Level from example design)

Ethernet 1000BASE-X PCS/PMA

or SGMII LogiCORE

BUFG

pma_rx_clk0

pma_rx_clk1

IOB LOGIC

IBUFG

pma_rx_clk0

IDELAY IPAD

		IOB LOGIC
	rx_code_group0_reg[0]	IDDR
rx_code_group0[0]		Q1

	rx_code_group1_reg[0]	D	IDELAY
rx_code_group1[0]		Q2
		C

IBUF

IPAD

rx_code_group[0]

Figure 6-4:Ten-Bit Interface Receiver Logic - Virtex-4 Device (Example Design)

Ethernet 1000BASE-X PCS/PMA or SGMII v9.1 www.xilinx.com 73

UG155 March 24, 2008