I'm developing a measurement application with the TI MSP430 and I would like to hear some suggestions on what type of memory I can use.
The idea is to use it for logging during a certain time and then download the data to a PC when the device is connected via USB. The estimate is to hold up to 5MB of data, every sample being around 25 bytes of data.
Would a simple EEPROM chip do or is there something better out there?
I've used the AT45D series of serial flash chips. They have an internal SRAM buffer to setup a page for erase/programming. SPI interface to read data in and out.
5MByte is a lot of data to store. Reading it out over USB implies that you are using one of the new parts with the USB device interface built in. If not then you are going to be using a USB to serial converter (FTDI or similar) and will be limited to the async serial data rates for reading the data out.
Have you considered connecting an SD memory card to the MSP, storing the data in that and then moving the card to the pc for reading the stored data. I have not written an interface to this device but there are plenty that have.
Serial flash is superior to EEPROM in this application. Atmel makes a great lineup. Your choice will depend largely on two things: (1) Your need to edit/sector your logs on the micro and (2) Your RAM availability on the MSP430.
Flash, unlike EEPROM, can only be written from a 1 to a 0. Changing the data from 0 to 1 requires erasing a section of the part, which is typically only available for pages or blocks of data. You'll need to buffer this page into RAM, erase the page, make your edit in RAM, and then write it back if you want to change something.
The AT45D series, as has been already pointed out, offers a number of parts which have RAM buffers on the chip to facilitate this process without using RAM on the microcontroller.
In the end, the entire series is pin-compatible, so just put down an 8-SOIC (150mil) footprint, and then you can swap out the parts if you need different options later.
I would suggest the AT25D series since it appears a little easier to use than the AT45D. Although it's a little slower and does not offer as many data transfer options or the SRAM buffers. It does have the advantage of being less expensive and it is still quick enough for most applications like data logging.
If you need 5MB of data it's unlikely that an EEPROM will work since they come in < 1Mbit packages typically. Flash chips from Atmel support up to 64-mbit or 8MB.
[This is in response to the comments following Ian's answer].
An SD card is just an SPI device, so there's no chip/interface necessary. Other protocols include a 2-wire interface (like I2C) and a 4-wire interface (with a complex CRC), but SPI is the most commonly used.
There is an SD card application note available for the MSP430 from TI here. It's brief, but it includes sample code. It handles reading and writing to various sectors on the SD card, which may be all you want if you're not going to plug it into a PC. Also look at these implementations by Foust (recommended) or Evans from MSU.
Once you have the basic functions to read and write a sector, you can either abstract a simple, custom filesystem over USB, or use an existing filesystem library. FatFS, EFSL, or DOSFs are all options for the latter. If implementing all of the required functions seems too hard, remember that all but a few can/will be stubs.
However, the file system will be abstracted through your USB interface to a degree. This will be easier if you have a real filesystem library and your card is in a readable filesystem, but that takes work. If you want to write your own "Filesystem" and save work/time/memory for the USB implementation, you can make its definition as simple and inflexible as log 1 starts at 0x0, log 2 starts at 0x10 0000, log 3 at 0x20 0000, and log 4 at 0x30 0000. Then, you can send this data over USB.
The USB interface can be as complex as you like it to be - from serial interface to mass storage device.
