MSP430G2744 : SPI Moduule performance @ 1.8V operational volatage.

Hi sri-sri,

Datasheet section 5.4 that you show above shows the active mode current consumption (typical) at 2.2 and 3V with a 1MHz DCO. Unfortunately we do not spec the device for every voltage and frequency combination because that would mean so many variables to include. However, we do below provide a graph (figure 5-2 in the datasheet) that shows some curves for the active mode current at differenct Vcc and with different DCO frequencies:

I know that this doesn't show 4.5MHz DCO frequency (this is an unusual frequency - the curves show the frequencies that have DCO calibration constants provided in INFOA, which are typically what people use) - but you could get an idea of what kind of range you would see.

For section 5.26 USCI SPI Master mode:

This table shows some critical SPI timings in the device that you have to consider when calculating the maximum SPI clock frequency supported by the device. I know that they say 3V in the datasheet, but if I were you I would probably use the min and max given in my SPI frequency calculation, and then leave myself some extra margin (set my SPI frequency a bit slower than that). You want your SPI frequency to be lower than  your operating frequency anyway most likely because your SPI receive and transmit buffers are only 1 byte, and you are going to have to have your CPU handling the data as well.

For calculating your maximum SPI clock frequency, you have to use the calculation from Footnote (1) on section 5.26:

"(1) fUCxCLK = 1/2tLO/HI with tLO/HI ≥ max(tVALID,MO(USCI) + tSU,SI(Slave), tSU,MI(USCI) + tVALID,SO(Slave)).

For the slave parameters tSU,SI(Slave) and tVALID,SO(Slave), see the SPI parameters of the attached slave."

You will have to look at the datasheet for whatever slave device you are talking to in order to find some of these parameters - namely the slave setup tSU,SI and valid tVALID,SO times. If your slave device has different You can also find some other threads like this one covering it: https://e2e.ti.com/support/microcontrollers/msp430/f/166/p/203168/721572#721572

Note that even for a G6744 master talking to another G2744 slave, the maximum SPI frequency would be:

max(tVALID,MO + tSU,SI, tSU,MI + tVALID,SO) = max(20ns+ 15ns, 75ns +75ns) = 150ns.

1/(2*150ns) = 3.33MHz.

I hope that this helps to clear things up!

Regards,

Katie