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7 Series FPGAs SelectIO Resources User Guide www.xilinx.com 151
UG471 (v1.5) May 15, 2015
Input Serial-to-Parallel Logic Resources (ISERDESE2)
The only valid clocking arrangements for the ISERDESE2 block using the networking
interface type are:
CLK driven by BUFIO, CLKDIV driven by BUFR
CLK driven by MMCM or PLL, CLKDIV driven by CLKOUT[0:6] of same MMCM or
PLL
CLK driven by BUFG, CLKDIV driven by a different BUFG
When using a MMCM to drive the CLK and CLKDIV of the ISERDESE2, the buffer types
suppling the ISERDESE2 can not be mixed. For example, if CLK is driven by a BUFG, then
CLKDIV must be driven by a BUFG as well. Alternatively, the MMCM can drive the
ISERDESE2 though a BUFIO and BUFR.
MEMORY Interface Type
The only valid clocking arrangements for the ISERDESE2 block using the memory
interface type are:
CLK driven by BUFIO, OCLK driven by BUFIO, and CLKDIV driven by BUFR
CLK driven by MMCM or PLL, OCLK driven by MMCM or PLL, and CLKDIV driven
by CLKOUT[0:6] of same MMCM or PLL
CLK driven by BUFG, OCLK driven by a BUFG, CLKDIV driven by a different BUFG
The OCLK and CLKDIV inputs must be nominally phase-aligned. No phase relationship
between CLK and OCLK is expected. Calibration must be performed for reliable data
transfer from CLK to OCLK domain. High-Speed Clock for Strobe-Based Memory
Interfaces and Oversampling Mode - OCLK gives further information about transferring
data between CLK and OCLK.
MEMORY_QDR Interface Type
The MEMORY_QDR mode has a complex clocking structure as a result of the QDR
memory requirements. This INTERFACE_TYPE attribute setting is only supported when
using the MIG tool.
OVERSAMPLE Interface Type
The OVERSAMPLE mode is used to capture two phases DDR data. Figure 3-7 shows a
more detailed logical representation of the ISERDESE2 and how data is captured on both
the rising and falling edge of CLK and OCLK. As shown in Figure 3-7, there must be a
90°offset phase relationship between CLK and OCLK as the data is captured on both CLK
and OCLK but is clocked out of the ISERDESE2 on the CLK domain. CLKDIV is not used
X-Ref Target - Figure 3-6
Figure 3-6: Clocking Arrangement Using BUFIO and BUFR
BUFIO
Clock
Input
ug471_c3_06_080310
BUFR (
÷
X)
ISERDESE2
CLK
CLKDIV
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