Device Configuration User Guide: Agilex™ 5 FPGAs and SoCs

ID 813773
Date 4/01/2024
Public

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3.2.5.2. Maximum Allowable External nCSO Pin Skew Delay Guidelines

Use the following equations to determine the skew between nCSO and AS_CLK:

  1. Skew (Tbd_clk – Tbd_ncso) > Tsu_ncso – Tdcsfrs
  2. Skew (Tbd_clk – Tbd_ncso) < AS_CLK/2 + Tdcslst – Tho_ncso

Hence, the allowable range for skew between nCSO and AS_CLK is as follows:

Tsu_ncso - Tdcsfrs < Skew (Tbd_clk – Tbd_ncso) < AS_CLK/2 + Tdcslst - Tho_ncso

  • Tsu_ncso = Chip select setup time required by the quad SPI flash. Refer to your quad SPI flash datasheet.
  • Tho_ncso = Chip select hold time required by the quad SPI flash. Refer to your quad SPI flash datasheet.
  • Tdcsfrs = AS_nCSO[3:0] asserted to first AS_CLK edge. Refer to the AS configuration timing specifications in the Agilex™ 5 Device Data Sheet.
  • Tdcslst = Last AS_CLK edge to AS_nCSO[3:0] deasserted. Refer to the AS configuration timing specifications in the Agilex™ 5 Device Data Sheet.
  • AS_CLK = AS_CLK clock period.

Example to Determine the Skew for 1 GB Quad SPI Flash Devices

Tsu_ncso = 2.7 ns

Tho_ncso = 3.375 ns

Tdcsfrs = 8.5 ns

Tdcslst = 6.8 ns

AS_CLK = 6.024 ns (166 MHz)

  1. Skew (Tbd_clk – Tbd_ncso) > Tsu_ncso – Tdcsfrs

    Skew (Tbd_clk – Tbd_ncso) > 2.7 – 8.5

    Skew (Tbd_clk – Tbd_ncso) > –5.8 ns

  2. Skew (Tbd_clk – Tbd_ncso) < AS_CLK/2 + Tdcslst – Tho_ncso

    Skew (Tbd_clk – Tbd_ncso) < 6.024/2 + 6.8 – 3.375

    Skew (Tbd_clk – Tbd_ncso) < 6.437 ns

The allowable range for skew between nCSO and AS_CLK is -5.8 ns < Skew (Tbd_clk – Tbd_ncso) < 6.437 ns