Electrical – SPI master and slave operating frequency

frequencyoscillatorspi

If a master is operating at 4MHz and the slave is at 16MHz the data should still be sampled at the speed of the SCLK pin, the frequency difference shouldn't matter right?

I used a Mikroe Dev board and tried to communicate to a CAN peripheral using SPI.
The board module operated @ 16MHz using a external oscillator while my MCU only used its internal 4MHz clock no commands worked until an external oscillator was used at 16MHz.

Can a master and slave operate at two different frequencies not the SCLK pin frequencies but the actual clock cycles frequency?

Best Answer

It comes down to the speed of the peripheral you are trying to interface to. In general the microprocessor or port is at a multiple of the CAN frequency.

You have no problem communicating between SPI master to MCP2251. But 4MHz master would mean 500kHz (divide by 8) CAN-BUS peripheral. Odds are CAN peripheral did not recognize communications if it was 1MHz (or 250kHz).

Your microprocesor was attempting to communicate with a peripheral at a slower rate than the peripheral expected.

Odds are the peripheral can be reconfigured to communicate at the lower speed if you need.

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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.

Electronic – Operating frequency of microcontroller PIC18f4550

Every register in the microcontroller exists whether you explicitly set a value or not. If you don't explicitly change the value of a register, the microcontroller will happily use the default value. The default values for each and every bit are defined in the datasheet.

For Microchip products, the default bit values for each register are defined along the top of the register description. See the red circled-area in the screen capture below. The OSCCON register defaults to a value of \$0100?000_2\$. The ? represents a read-only bit that has no default value upon power up. Looking at just the Internal Oscillator Frequency Select bits, IRCF, the default bits are \$100_2\$. So your default frequency is 1MHz.

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Best Answer

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Electronic – Operating frequency of microcontroller PIC18f4550

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