Visible to Intel only — GUID: iga1401314934061
Ixiasoft
Visible to Intel only — GUID: iga1401314934061
Ixiasoft
33.7.4. Example Calculation
Parameter | Symbol | Value (ns) in -7 Speed Grade | ||
---|---|---|---|---|
Min. | Max. | |||
Access time from CLK (pos. edge) | CL = 3 | tAC(3) | — | 5.5 |
CL = 2 | tAC(2) | — | 8 | |
CL = 1 | tAC(1) | — | 17 | |
Address hold time | tAH | 1 | — | |
Address setup time | tAS | 2 | — | |
CLK high-level width | tCH | 2.75 | — | |
CLK low-level width | tCL | 2.75 | — | |
Clock cycle time | CL = 3 | tCK(3) | 7 | — |
CL = 2 | tCK(2) | 10 | — | |
CL = 1 | tCK(1) | 20 | — | |
CKE hold time | tCKH | 1 | — | |
CKE setup time | tCKS | 2 | — | |
CS#, RAS#, CAS#, WE#, DQM hold time | tCMH | 1 | — | |
CS#, RAS#, CAS#, WE#, DQM setup time | tCMS | 2 | — | |
Data-in hold time | tDH | 1 | ||
Data-in setup time | tDS | 2 | ||
Data-out high-impedance time | CL = 3 | tHZ(3) | 5.5 | |
CL = 2 | tHZ(2) | — | 8 | |
CL = 1 | tHZ(1) | — | 17 | |
Data-out low-impedance time | tLZ | 1 | — | |
Data-out hold time | tOH | 2.5 |
The FPGA I/O Timing Parameters table below shows the relevant timing information, obtained from the Timing Analyzer section of the Quartus® Prime Compilation Report. The values in the table are the maximum or minimum values among all device pins related to the SDRAM. The variance in timing between the SDRAM pins on the device is small (less than 100 ps) because the registers for these signals are placed in the I/O cell.
Parameter | Symbol | Value (ns) |
---|---|---|
Clock period | tCLK | 20 |
Minimum clock-to-output time | tCO_MIN | 2.399 |
Maximum clock-to-output time | tCO_MAX | 2.477 |
Maximum hold time after clock | tH_MAX | –5.607 |
Maximum setup time before clock | tSU_MAX | 5.936 |
You must compile the design in the Quartus® Prime software to obtain the I/O timing information for the design. Although Intel FPGA device family datasheets contain generic I/O timing information for each device, the Quartus® Prime Compilation Report provides the most precise timing information for your specific design.
The timing values found in the compilation report can change, depending on fitting, pin location, and other Quartus® Prime logic settings. When you recompile the design in the Quartus® Prime software, verify that the I/O timing has not changed significantly.
The following examples illustrate the calculations from figures Maximum SDRAM Clock Lag and Maximum Lead also using the values from the Timing Parameters and FPGA I/O Timing Parameters table.
The SDRAM clock can lag the controller clock by the lesser of Read Lag or Write Lag:
Read Lag = tOH(SDRAM) – tH_MAX(FPGA)
= 2.5 ns – (–5.607 ns) = 8.107 ns
or
Write Lag = tCLK – tCO_MAX(FPGA) – tDS(SDRAM)
= 20 ns – 2.477 ns – 2 ns = 15.523 ns
The SDRAM clock can lead the controller clock by the lesser of Read Lead or Write Lead:
Read Lead = tCO_MIN(FPGA) – tDH(SDRAM)
= 2.399 ns – 1.0 ns = 1.399 ns
or
Write Lead = tCLK – tHZ(3)(SDRAM) – tSU_MAX(FPGA)
= 20 ns – 5.5 ns – 5.936 ns = 8.564 ns
Therefore, for this example you can shift the phase of the SDRAM clock from –8.107 ns to 1.399 ns relative to the controller clock. Choosing a phase shift in the middle of this window results in the value (–8.107 + 1.399)/2 = –3.35 ns.