Erik:

The SiLabs data sheet for the C8051F020 clearly states that one uses MOVX to write FLASH when the enable bits are set in the flash control register. It also states that MOVC is used to read FLASH and it states that MOVX reads always will read the XRAM. The stated behavior offers the flexibility to use XRAM data buffers to hold FLASH contents during programming operations. This can be a really really important consideration for certain embedded applications using this part if certain parts of the FLASH want to have only a small portion updated. The 512 byte erase block size on this part requires a RAM buffer of at least 512 bytes to support saving the previous content of a FLASH block while the whole block is erased and then re-written with just a small portion changed. This behavior is also needed for various FLASH management algorithms that "write to fill a block" that then require a flash block content to be copied to another already erased block.

Michael Karas