The TX/RXOUTCLK are routed to the FPGA logic through a mixed-mode clock manager (MMCM) or BUFG. An MMCM is needed when the TXUSRCLK does not match TXUSRCLK2 and the RXUSRCLK does not match RXUSRCLK2. Table: MMCM for TX Buffer Bypass and Table: MMCM for RX Buffer Bypass capture various scenarios to instantiate an MMCM.
Table 3-4: MMCM for TX Buffer Bypass
TX External Data Width
|
TX Internal Data Width
|
TX Buffer Bypassed
|
Source for TXOUTCLK
|
TXUSRCLK2
|
MMCM
|
16
|
16/20
|
No
|
TXOUTCLKPMA
|
TXUSRCLK
|
No
|
32
|
16/20
|
No
|
TXOUTCLKPMA
|
TXUSRCLK/2
|
Yes
|
32
|
32/40
|
No
|
TXOUTCLKPMA
|
TXUSRCLK
|
No
|
64
|
32/40
|
No
|
TXOUTCLKPMA
|
TXUSRCLK/2
|
Yes
|
20
|
20
|
No
|
TXOUTCLKPMA
|
TXUSRCLK
|
No
|
40
|
20
|
No
|
TXOUTCLKPMA
|
TXUSRCLK/2
|
Yes
|
40
|
40
|
No
|
TXOUTCLKPMA
|
TXUSRCLK
|
No
|
80
|
40
|
No
|
TXOUTCLKPMA
|
TXUSRCLK/2
|
Yes
|
16
|
16/20
|
Yes/No
|
Ref Clk
If Refclk = TXUSRCLK2 then
Wizard chooses TXPLLREFCLK_DIV1
as TXOUTCLK
Else
Wizard chooses TXPLLREFCLK_DIV2
As TXOUTCLK
You should choose the appropriate REFCLK to meet the preceding criteria.
|
TXUSRCLK
|
No
|
32
|
16/20
|
Yes/No
|
TXUSRCLK/2
|
Yes
|
32
|
32/40
|
Yes/No
|
TXUSRCLK
|
No
|
64
|
32/40
|
Yes/No
|
TXUSRCLK/2
|
Yes
|
20
|
20
|
Yes/No
|
TXUSRCLK
|
No
|
40
|
20
|
Yes/No
|
TXUSRCLK/2
|
Yes
|
40
|
40
|
Yes/No
|
TXUSRCLK
|
No
|
80
|
40
|
Yes/No
|
TXUSRCLK/2
|
Yes
|
Table 3-5: MMCM for RX Buffer Bypass
RX External Data width
|
RX Internal Data Width
|
RX Buffer Bypassed
|
Source for RXOUTCLK
|
RXUSRCLK2
|
MMCM
|
16
|
16/20
|
No
|
RXOUTCLKPMA/TXOUTCLK/REFCLK
|
RXUSRCLK
|
No
|
32
|
16/20
|
No
|
RXOUTCLKPMA/TXOUTCLK/REFCLK
|
RXUSRCLK/2
|
Yes
|
32
|
32/40
|
No
|
RXOUTCLKPMA/TXOUTCLK/REFCLK
|
RXUSRCLK
|
No
|
64
|
32/40
|
No
|
RXOUTCLKPMA/TXOUTCLK/REFCLK
|
RXUSRCLK/2
|
Yes
|
20
|
20
|
No
|
RXOUTCLKPMA/TXOUTCLK/REFCLK
|
RXUSRCLK
|
No
|
40
|
20
|
No
|
RXOUTCLKPMA/TXOUTCLK/REFCLK
|
RXUSRCLK/2
|
Yes
|
40
|
40
|
No
|
RXOUTCLKPMA/TXOUTCLK/REFCLK
|
RXUSRCLK
|
No
|
80
|
40
|
No
|
RXOUTCLKPMA/TXOUTCLK/REFCLK
|
RXUSRCLK/2
|
Yes
|
16
|
16/20
|
Yes
|
RXOUTCLKPMA
|
RXUSRCLK
|
No
|
32
|
16/20
|
Yes
|
RXUSRCLK/2
|
Yes
|
32
|
32/40
|
Yes
|
RXUSRCLK
|
No
|
64
|
32/40
|
Yes
|
RXUSRCLK/2
|
Yes
|
20
|
20
|
Yes
|
RXUSRCLK
|
No
|
40
|
20
|
Yes
|
RXUSRCLK/2
|
Yes
|
40
|
40
|
Yes
|
RXUSRCLK
|
No
|
80
|
40
|
Yes
|
RXUSRCLK/2
|
Yes
|