Electronic – Maximum SPI clock speed specified in data sheet

clock-speedspi

For integrated circuits that use SPI interface, they specify maximum clock frequency in their datasheets such as attached below.

The question is that if the datasheet speficies the maximum frequency as 6MHz, can I decide that it will be safe to set up clock speed exactly at 6MHz(accuracy determined by crystal used for MCU)? Or It is safer to have some margin?

Best Answer

No, 6 MHz is guaranteed to work by the specification.

In practice you will very likely find devices which can work up to 8 or even 10 MHz. But it is not guaranteed that that will always work for all power supply voltages, temperatures and all chips from any batch.

The 6 MHz however is guaranteed over all conditions. So no, you do not need a margin as long as your 6 MHz is accurate enough (and it probably will be as it is usually derived from a crystal based clock).

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Electronic – SPI flash memory doesn’t work without huge delays

What concerns me is your disregard for EMC issues in your design when it uses 2" of 24AWG wire for signal wiring without mentioning any ground planes.

A systematic approach must be considered in communication of all signals to determine, which need shielding, common mode filter, ground plane, star ground, radial ground and impedance control on high speed signals.

Can you obtain some low capacitance FET probes or better yet, Tektronix differential FET Probes and scope the clock & data signals at both ends?

Also remember the specs only say 80MHz is MAX and THERE IS NO MIN. Also Maximum clock frequency for Read Instruction, 03H, is 33 MHz in the fine print for this 80MHz part. (darn those marketing guys)

THings to do to improve performance;

Use AWG30 twisted pair 12 turns/ft for every signal to this chip where you need better shielding and less overshoot ripple.
Have a dedicated regulator @ Vdd @ 3.6V for both IC's. Notice there is no spec for the 80MHz part yet the 66MHz part says VDD = 3.0 - 3.6 V, CL = 15 pF, so I would use Vmax=3.6 to get as much performance as possible. (darn those ambiguous specs)
Verify all voltage levels, rise times and setup times.

Electronic – Arduino SPI Clock Speed Configuration

You can set the SPI speed (and many other things!) using the Arduino SPI library without specifying any register values. You already did it with MSBFIRST. Like so:

  SPI.setDataMode(SPI_MODE3);
  SPI.setBitOrder(MSBFIRST);
  SPI.setClockDivider(SPI_CLOCK_DIV4); // 16/4 MHz
  SPI.begin();

Also, SPI.begin sets all the pin modes for you, so no need to do that.

Best Answer

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