Assembly之Instruction之Byte and Word

 

Byte and word issues

　　The MSP430 is byte-addressed, and little-endian. Word operands must be located at even addresses

1　　Appending “.b” to an instruction makes it a byte operation.

　　A byte instruction with a register destination clears the high 8 bits of the register to 0. Thus, the following would clear the top byte of the register, leaving the lower byte unchanged:

mov.b Rn,Rn

 

2　　Adding ".w"(or nothing) to an instruction makes it a word operation, which is also the default behaviour.

 

3　　Peripherals are divided into an 8-bit bank and a 16-bit bank.

　　 The 8-bit peripherals must only be accessed using 8-bit instructions; using a 16-bit access produces garbage in the high byte.

　　 The 16-bit peripherals must only be accessed at even addresses. Byte accesses to even addresses are legal, but not usually useful.