Interfacing mspf5438 with microcontroller

The most basic way is via serial communication. You can use SPI, I2C if there is a "master" or normal RS-232/UART if you prefer or need bidirectional communication. Any of these can be realized with you MSP. One thing to remember is, that your system had equal supply voltage levels or that you need to take care of level translation when interfacing for example a 5V system.

"Full" RS-232 would have level shifters as MAX232 or MAX3232 to bring logic levels to RS232 levels (and invert them) of +/- 15V - but one can easy omit them, if both systems use the same levels.

Can 89C51 directly read from the memory of  MSPF5438??

No, as an MSP does not have an outside memory bus where you could attach. So you need to go via some interface somehow. Of course you could build an memory bus interface with the port pins - but that's a waste of pins. 

Think about it: the MSP430 neither knows nor cares what is attached to its interfaces; it just sends stuff to them, and receives stuff from them - it is irrelevant where the sent stuff goes to, and where the received stuff comes from.

So you can use any interface you like - so long as both devices can support it.

As already noted, the async serial link is probably the commonest; but there's also SPI, I2C, etc, etc,...

Or you can devise your own bit-bashed serial or parallel interface...

Andy Neil said:

Or you can devise your own bit-bashed serial or parallel interface...

As matter of fact, there's an interesting implementation of MCU-to-MCU DMA transfer between two MSP430s that mimics a parallel bits strobe interface using TimerA and GPIOs. If you can sync your MCU with the MSP430 (eg clock both with MCLK) then theoretically you can get a byte transfer every two cycles (from the MSP430).

Of course this does not include any protocol/sync overhead, error correction and detection, IO and DMA capability of the other controller, Endian-ness, etc etc...

See Peters, D et al. 2009. "An Energy Efficient Parallel Embedded System for Small Satellite Applications". ISAST Transactions on Computers and Intelligent Systems. 2(1):8-16.

http://www.isastorganization.org/ISAST_CIS0101.pdf

Tony