
Ports and Attributes
The following table defines the reference clock input ports in the IBUFDS_GTM software
primitive.
Table 3: Reference Clock Input Ports (IBUFDS_GTM)
Port
Dir
Clock Domain
Description
CEB
In
N/A
This is the active-Low asynchronous clock enable signal for the clock buffer.
Setting this signal High powers down the clock buffer.
I
In (pad)
N/A
These are the reference clock input ports that get mapped to GTREFCLKP.
IB
In (pad)
N/A
These are the reference clock input ports that get mapped to GTREFCLKN.
O
Out
N/A
This output drives the GTREFCLK signal in the GTM_DUAL software primitive.
Reference Clock Selection and Distribution
for more details.
ODIV2
Out
N/A
This output can be configured to output either the O signal or a divide-by-2
version of the O signal. It can drive the BUFG_GT via the HROW routing. Refer
Reference Clock Selection and Distribution
for more details.
The following table defines the attributes in the IBUFDS_GTM software primitive that configure
the reference clock input.
Table 4: Reference Clock Input Attributes (IBUFDS_GTM)
Attribute
Type
Description
REFCLK_EN_TX_PATH
1-bit
Reserved. This attribute must always be set to
1'b0
.
REFCLK_HROW_CK_SEL
2-bit
Configures the ODIV2 output port:
2'b00
: ODIV2 = O.
2'b01
: ODIV2 = Divide-by-2 version of O.
2'b10
: ODIV2 =
1'b0
.
2'b11
: ODIV2 = Reserved.
REFCLK_ICNTL_RX
2-bit
Reserved. Use the recommended value from the Wizard.
Output Mode
The reference clock output mode can be accessed via the OBUFDS_GTM software primitive. The
reference clock output mode structure for the OBUFDS_GTM primitive is shown in the following
figure. The ports and attributes controlling the reference clock output are tied to the
OBUFDS_GTM software primitive.
Chapter 2: Shared Features
UG581 (v1.0) January 4, 2019
Virtex Ult GTM Transceivers
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