MSP430F5659: SPI communication with other device not from TI

Hi Jongchan!

Of course you can use the MSP430 with non-TI parts. You have to take care of the signal levels - what is the supply voltage of the MSP? It would be best if sensor and microcontroller would work with the same voltage level, of course. Otherwise level translators might be necessary. Look at this table for the threshold voltages:

Same thing for your sensor - if it is powered with 1.8V and will receive a SPI signal of 3.3V, excessive current might flow into the device. In some cases you can work with a simple series resistor. Maybe you want to tell about the sensor you want to use and the supply voltages.

Dennis

The table says that at 3V the MSP might expect a logic high level up to 2.1V in the worst case (device dependent). At 3.3V this will be even higher. 1.8V might work, but there is no guarantee. And you will have the problem with the sensor that might not like being driven by 3.3V while powered by 1.8V - you may want to use a level converter or do some level shifting by yourself.

SPI is 8 bit per transmission - you will see that slaves normally have 8 bit or multiples of 8 bits to read or write. For a 16 bit adc result, for example, you have to receive two times 8 bits and combine the data to a 16 bit word inside your controller. Same for 24, 32 or 64 bits of data.

A 16 bit word could look like this:

MSB -> 1101 1001 1011 0000 <- LSB

If you request the data you normally get the MSB first, so you could do something like this:

// Data: MSB -> 1101 1001 1011 0000 <- LSB

uint8_t data_buffer[2];
uint16_t data_word = 0;

data_buffer[0] = <request MSB>; // 1101 1001
data_buffer[1] = <request LSB>; // 1011 0000

data_word = data_buffer[0];     // 0000 0000 1101 1001
data_word <<= 8;                // 1101 1001 0000 0000
data_word |= data_buffer[1];    // 1101 1001 1011 0000

Dennis

What I mean there are significant delay between reading/writing between two 8-bit data as shown the above figure.

The figure shows the clk signal in SPI communication. clk goes up and down only if there is a data transfer so each yellow bar corresponds to 8-bit data transfer.

In this figure, there are quite a big delay between each bars, which means that msp cannot get any data in this time. Since our receiver device continuously convert analog data into digital data, there should be some missing data.