Questions on MSP430 about Program Counter, constant generator and bootstrap loader

[binhjuventus]

I'm reading a book on MSP430

1. There's a phrase I do not understand:

The Program Counter is located in R0. Since individual memory location addresses are 8-bit, but all instructions are 16 bit, the PC is constrained to even numbers (i.e. the LSB of the PC is always zero).

Why does Program Counter (PC) increment by 2 not by 1?

2. R2 and R3 act as a constant generators, what are the roles of constant generator? We can generate a constant by using an instruction like ADD or MOV?

3. What is bootstrap loader?

I'm beginner so maybe these questions are trivial to you but It would be very kind of you to clarify these to me.
Thanks in advance!

 

[suryakant]

Re: Questions on MSP430

1. Memory addresses are 8 bit. But any instruction in MSP requires 16 bit, so it will occupy two 8 bit locations (8 bit+ 8bit)... e.g. if instructions starts at address 0000 then first instruction will occupy 0000 and 0001 location, so obviously next instruction will start at 0002

This way PC is always constrained to even numbers..


2. R2, R3 generates commonly used constants in program... e.g 0, 1, 0xFFFF etc...
we can use MOV instruction, but it ll take more memory as these constant will appear as operands..
e.g.

OPCODE
OPERAND VALUE (00 or 01 or 0xffff)

instead in MSP these are encoded in the instruction only...
e.g.
OPCODE

only
so it saves code..

also as we know register access is faster than memory access, so this saves time....

3.
The intention of the bootstrap loader is to download data into the flash memory module.

For programming MSP430 u require programmer ... But by using BootStrap loader u can program the MSP remotely on serial communication... u can say remote firmware upgradation via serial ...