MSP430FR2000: MSP430FR xxxx - how slow can you operate the SPI bus

Hi Dan,

So sorry for late replying.

Let me give a quick device selection with your requirements, which I locked the first one to 32k FRAM

1) at least 32k FRAM  -- [Wei] checking with 32k FRAM

2) 2kx8k ram (not sure on exact size)

3) two uarts

4) at least one I2C

5) at least one SPI

There are 8 part matching above requirements as below in the selection tool. I assume you don't need the LCD driver on chip, so that the selected part could be MSP430FR2355/2155 and MSP430FR5870/5970. 

This result should only be a quick suggestion since we need more detailed requirements, such as device package, pin count(general GPIO usage), exact RAM size(the largest RAM size with 32k FRAM could be 4k), any other peripherals and the target price.

Please let me know if you could get more requirements and then I could help you to give a better suggestion.

For other questions:

    Need to have the cpu running very low power. It never sleeps.  clock speed might be 32.768 khz or slower.

 [Wei] Yes, you can do this.

I would like to take the MSP430FR2xx&4xx family as an example. You could see the Clock System diagram on the Figure3-1&2 of the User's Guide. MCLK could be sourced by DCOCLKDIV/REFOCLK/XT1/VLO, which the REFOCLK/XT1 is 32.768 kHz and VLO is a typical 10kHz clock. The MSP430FR5xx&6xx family also support the 32.768kHz or VLO to source the MCLK

    Just wondering how slow can you operate a SPI buss?  Can you have a 1khz clock talking to an external FRAM memory chip?

[Wei] I just checked the datasheet for SPI clock frequency, it doesn't say the MIN value. I would like to double check if any limitation for lowest SPI clock frequency with our design team tomorrow morning(China time) when I get to office.

Do you say that you need the MCU connecting with an external FRAM via SPI interface?

Hi Dan,

Additional reply based on confirmation with our design team. 

Just wondering how slow can you operate a SPI buss?  Can you have a 1khz clock talking to an external FRAM memory chip?

[Wei] I just checked the datasheet for SPI clock frequency, it doesn't say the MIN value. I would like to double check if any limitation for lowest SPI clock frequency with our design team tomorrow morning(China time) when I get to office.

Do you say that you need the MCU connecting with an external FRAM via SPI interface?

[Wei] The SPI clock is edge triggered, so that there is no lowest limitation for clock frequency.

For the part suggestion, I would like to give you a better selection with more detailed requirements. You could also use the products selection tool to filtrate by various of requirements, such as memory size, peripherals, GPIO, package, sub-family, approx price, and so on.