C5515 SPI Timing not as stated in Datasheet (Output hold time, SPI_CS inactive to SPI_CLK)

Sasha Kalmanovich

In page 131 of DSP Datasheet, Time number 3 :

Output hold time, SPI_CS inactive to SPI_CLK toh(SCLKI-SPICSI) inactive = 0.5tC - 2.2.

We work in System Clock = 40 Mhz, SPI bus clock = 40/6 = 6.66 Mhz.

The time we measure is much smaller than stated in Datasheet - about 50 ns,while according to datasheet it should be 72 ns.

Any ideas ?

Thanks.

over 13 years ago

0 Steve Tsang over 13 years ago

TI__Mastermind 23785 points

The datasheet numbers are for the full recommended operating conditions on section 5.2.

Regards.

0 Sasha Kalmanovich over 13 years ago in reply to Steve Tsang

Intellectual 840 points

Hello Steve.

We are under recommended conditions of section 5.2. namely: System Clock = 40 Mhz, SPI bus clock = 40/6 = 6.66 Mhz .

Table 6-46 Switching characteristics of SPI bus defines time 3 ( Output hold time, SPI_CS inactive to SPI_CLK oh(SCLKI-SPICSI)) as (0.5tc-2.2) minimum

This time depends only on Tc clock (SPI clock). So, according to the data sheet t3 should be approx.. 73ns. But we get 50ns.

Could you explain why it happened ?

Will this violation affect SPI module of DSP during DSP read access over SPI?

0 Steve Tsang over 13 years ago in reply to Sasha Kalmanovich

TI__Mastermind 23785 points

This is too fast. The consideration here for the read access is timing parameter #8 during mode 1 & 3, which is 0 min. So this is not affected.

Regards.

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C5515 SPI Timing not as stated in Datasheet (Output hold time, SPI_CS inactive to SPI_CLK)