Mmc_Clk/Spi_Clk High-/Low-Time Computation - Texas Instruments OMAP5910 Technical Reference Manual

MMC/SD Host Controller
Table 7–99. MMC_CLK/SPI_CLK High-/Low-Time Computation
Clk_Div MMC_CLK/SPI_CLK High-Time
1 ref_clk_high_time
Even ≥ 2
ref_clk_per (Clk_div/2)
Odd ≥ 3
ref_clk_per (TRUNC[Clk_div/2] + 1)
(POL=PHA)
Odd ≥ 3
ref_clk_per (TRUNC[Clk_div/2])
(POL≠PHA)
7-134
ref_clk_per is reference clock period (in ns) to the module (end-system
dependant).
TRUNC is the truncate to an integer number function (round down).
Example 1: Module reference clock = 48 MHz (20.83 ns), target is MMC card.
-
clk_div = 3 (MMC card is 20 MHz max).
-
MMC_CLK period = 62.5 ns (> 50 ns OK)
-
Ideal MMC_CLK high time = 41.66 ns (>>10 ns)
-
Ideal MMC_CLK low time = 20.83 ns (>>10 ns)
MMC_CLK/SPI_CLK Low-Time
ref_clk_low_time
ref_clk_per (Clk_div/2)
ref_clk_per (TRUNC[Clk_div/2])
ref_clk_per (TRUNC[Clk_div/2] + 1)