USCI SPI Instead of USART SPI

Jonthornham

Other Parts Discussed in Thread: MSP430G2533

I am working on a project where I would like to write large amounts of data to an SD card. I have found the following TI document http://www.ti.com/lit/an/slaa281b/slaa281b.pdf which discusses using USART SPI to write to an SD card. The MCU I am using (MSP430G2533) only offers USCI SPI. It seems to me that I should be able to use USCI SPI to communicate with an SD card based on the reading I've done. It's my first time using either so I was hoping someone could tell me if I am correct, or is there something I am missing?

Take care,

Jon

over 13 years ago

Jens-Michael Gross over 13 years ago

Guru 227245 points

The USCI is an improvement of the USART module.
They are not too different. However, there are differences.:

The I2C part is completely different.
The UART part has an oversampling mode and uses a simpler modulation configuration. Also supports automatic baudrate detection.

The main change on the SPI part is that the USCI can do SPI with full clock speed (sendign direction), while the USART can only with half speed.
There are some other changes in teh assembly of the config registers and the interrupt configuration. And th USCI has two SPI modules which can run simultaneously. And I'm not sure about the 4-wire mode (which you only need for slave or multimaster operation).
But on the bottom line, the SPI part has the least changes between USCI and USART.

Jon81 said:
I should be able to use USCI SPI to communicate with an SD card based on the reading I've done.

I did with both. On teh USART with 4MHz and on the USCI with 16MHz SPI clock. So i know it works. :)

Jonthornham over 13 years ago in reply to Jens-Michael Gross

Expert 1490 points

Jens-Michael Gross,

Awesome. Thank you kindly. I am glad to here you got it working with the USCI at 16MHz.

Take care,

Jon

Jonthornham over 13 years ago in reply to Jonthornham

Expert 1490 points

Jens-Micahel Gross,

Out of curiosity, when you were storing data on an SD card, were you also downloading the data to a computer through an SD slot/reader? I know the MSP430 will write raw data to the SD card. I am looking for a program to read the bytes so I can compile the data. If you used one that is publicly available could you please let me know what it's called.

Take care,

Jon

Jens-Michael Gross over 13 years ago in reply to Jonthornham

Guru 227245 points

Sorry, I never stored PC compatible data on the SD. I used a direct time->address conversion fo rstorigng the data, so i could put 1 year of measurements on an 1GB card without any overhead (only 512 bytes ram required for buffering the next segment to write).

The card was to be read in our access poitn which used the same firmware (except for the low level SPI access) and forwards the data upon request through a TCP connection.

If oyu want to be PC compatible on the MSP, you'll need an file system driver. Some of those exist. These drivers usually need you to provide a 'read segment' and 'write segment' function for the card access and require quite some memory for buffering (I think, 1-2k ram are minimum).
With such a file system driver, you will then have fopen/fwrite etc. available for your program.

On the other hand, i don't know abouthow to read raw data on the PC. I remember some programs to read low-level sectors on HDs (e.g. WinHex). But I'm not sure whether you can access an SD card at all if it doesn't have a proper formatting. Well, if your card reader has a drive letter even without a card inserted, you might be lucky.

Bernhard Weller over 13 years ago in reply to Jens-Michael Gross

Genius 4925 points

For reading raw data under windows you will need administrator privileges on anything newer than Windows XP. You can gain raw access using the Win32API functions. An example of doing so using C# is given here.

Now if I remember correctly you will indeed need a card reader with an assigned drive letter, but my card readers all give me drive letters even for unformatted cards, so that should be possible.

If you won't need to read data often, you can use HxD to get access to the raw data on your drives (I've not tried it with an SD card but I don't see why it shouldn't work as long as you get a drive letter)

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USCI SPI Instead of USART SPI