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120 www.xilinx.com 7 Series FPGAs SelectIO Resources User Guide
UG471 (v1.5) May 15, 2015
Chapter 2: SelectIO Logic Resources
IDELAYCTRL primitive must be instantiated. See IDELAYCTRL Usage and Design
Guidelines for more details. The control pins being used in VARIABLE mode are
described in Table 2-6.
Loadable variable delay mode (IDELAY_TYPE = VAR_LOAD)
In addition to having the same functionality of (IDELAY_TYPE = VARIABLE) in this
mode the IDELAY tap can be loaded via the 5-input bits CNTVALUEIN<4:0> from the
FPGA logic. When LD is pulsed the value present at CNTVALUEIN<4:0> will be the
new tap value. As a results of this functionality the IDELAY_VALUE attribute is
ignored. When used in this mode, the IDELAYCTRL primitive must be instantiated.
See IDELAYCTRL Usage and Design Guidelines for more details. The control pins
being used in VAR_LOAD mode are described in Table 2-7.
IDELAY Timing
Table 2-8 shows the IDELAY switching characteristics.
Table 2-6: Control Pin when IDELAY_TYPE = VARIABLE
CLDCEINC TAP Setting
0xxxNo Change
11xxIDELAY_VALUE
100xNo Change
1011Current Value
+1
1010Current Value
–1
1000No Change
Table 2-7: Control Pin when IDELAY_TYPE = VAR_LOAD
C LD CE INC CNTVALUEIN CNTVALUEOUT TAP Setting
0 x x x x No Change No Change
1 1 x x CNTVALUEIN CNTVALUEIN CNTVALUEIN
1 0 0 x x No Change No Change
1011 x Current Value +1 Current Value +1
1010 x Current Value1 Current Value1
1000 0 No Change No Change
Table 2-8: IDELAY Switching Characteristics
Symbol Description
T
IDELAYRESOLUTION
IDELAY tap resolution
T
ICECK
/T
ICKCE
CE pin Setup/Hold with respect to C
T
IINCCK
/T
ICKINC
INC pin Setup/Hold with respect to C
T
IRSTCK
/T
ICKRST
LD pin Setup/Hold with respect to C
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