DRA750: DRA75 QSPI read timing query

Nandhini KS

Part Number: DRA750

Hi,

We are using "DRA752BPGABCQ1" in our circuit and validating QSPI read timings. Can you please clarify read timing of the processor.

As per TRM (referring to table, page#), the processor clock reads the slave device data on every falling edge of the clock. Please refer to below datasheet timing expert.

The slave device (serial memory) send the data on falling edge and if processor also reads data on falling edge, the setup/holdtime can not be met. We captured actual circuit waveform and shared below.

Can you please clarify whether the processor reads the data on falling edge or rising edge of the clock?

thank you

over 6 years ago

0 Shravan Karthik over 6 years ago

TI__Genius 14650 points

Hi Nandhini,

By defaul clock mode 0 is used for QSPI.

Clock_mode_3 has a limitation which prevents operating at highest frequency (i916 in http://www.ti.com/lit/er/sprz426d/sprz426d.pdf).

Regards

Shravan

0 Nandhini KS over 6 years ago in reply to Shravan Karthik

Prodigy 250 points

Dear Shravan,

Thanks for your response.

Actually our query is "In SPI Mode 3 operation, whether the processor(@Master) reads the data on falling edge or rising edge of the clock"?

0 Brad Griffis over 6 years ago in reply to Nandhini KS

TI__Guru*** 125430 points

Nandhini,

For SPI Mode 3 it is sampled on the falling edge, but it's a full clock cycle later in order for the timings to work properly. Please have a look at the Technical Reference Manual Figure 24-101 "SPI Clock Modes" to understand better. Here's a snippet:

In particular, note that for Mode 3, the output data starts on the very first falling edge, but the input data begins on the second edge. This gives you nearly a full cycle time to meet setup requirements. In terms of hold time, you need to look at minimum output delay for each device. You need to ensure that the minimum output delay of the transmitting/output device is greater than the maximum required hold time of the input device. I expect most QSPI devices to be compatible with these timings.

Best regards,
Brad

0 Nandhini KS over 6 years ago in reply to Brad Griffis

Prodigy 250 points

Thank you Brad. Understood

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DRA750: DRA75 QSPI read timing query