ECP5 and ECP5-5G High-Speed I/O Interface
Technical Note
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FPGA-TN-02035-1.3
5.13.2.2.
Receive Aligned Interface
shows the data and clock relationship for a Receive Aligned Interface. The clock is aligned edge to edge the
data.
Receive Parameters
RDTCLK
Data (RDAT, RCTL)
t
DVACLKGDDR
t
DVECLKGDDR
t
DVECLKGDDR
t
DVACLKGDDR
Figure 5.17. RX Aligned Interface Timing
Note
: tDVA_GDDRX1/2 = Data Valid after CLK, tDVE_GDDRX1/2 = Data Hold After CLK
In this case, the worst case data may occur after the clock edge. Hence, it has a negative setup time when entering the
device. In this case, the worst case setup is specified by the tDVACLKGDDR after the clock edge and the worst case hold
time is specified as tDVECLKGDDR. For this case, the setup and hold time can be specified as –
INPUT_SETUP PORT “din” <-tDVA_GDDRX1/2 > ns HOLD < tDVE_GDDRX1/2> ns CLKPORT “clk”;
Note
: Negative number is used for SETUP time as the data occurs after the clock edge in this case.
The External Switching Characteristics section of
ECP5 and ECP5-5G Family Data Sheet (FPGA-DS-02012)
specifies the
MIN tDVA_GDDRX1/2 and tDVE_GDDRX1/2 values required for each of the high-speed interfaces running at MAX
speed. These values can be picked up from the data sheet if the interface is running at MAX speed. The data sheet
numbers for this preference is listed in ns + ½ UI (Unit Interface). 1 UI is equal to ½ the Clock Period. Hence, these
numbers need to be calculated from the CLK Period used.
Preference Example:
For GDDRX2_RX.ECLK.Aligned interface running at max speed of 400 MHz (UI = 1.25 ns)
tDVA_GDDRX2 = - 0.344 ns + ½ UI = 0.281 ns, tDVE_GDDRX2 = 0.344 ns + ½ UI =0.969 ns
The preference for this case would be –
INPUT_SETUP PORT "datain" -0.2810000 ns HOLD 0.969 ns CLKPORT "clk”;
Note
ECP5 and ECP5-5G Family Data Sheet (FPGA-DS-02012)
for the latest tDVA_GDDRX1/X2 and
tDVE_GDDRX1/X2 numbers.
5.13.2.3.
Receive Dynamic Interfaces
Static Timing Analysis does not show timing for all the dynamic interfaces cases as either the clock or the data delay is
dynamically updated at run time.
5.13.3.
DDR Clock to Out Constraints for Transmit Interfaces
All of the Transmit (TX) interfaces both x1 and x2 can be constrained with clock to out constraint to detect the
relationship between the clock and data when leaving the device.
shows how the clock to out is constrained in the software. Min tCO is the minimum time after the clock
edge transition that the data does not transition. Max tCO is the maximum time after clock transition before which the
data transitions. Therefore, any data transition must occur between the tCO Min and tCO Max values.