Flash Memory RAM or ROM

Hello Vinot,

Vinoth Ramalingam said:

I wish to know how the codes are stored in the memory.

Code is stored in flash memory. Flash isn't neither RAM nor ROM.

ROM is a "Read Only Memory". You can write flash memory so it's not ROM. There is no ROM in most MSP devices.

RAM needs to be refreshed so if you turn off the power you will lost your data. RAM is faster than flash so you can store there variables, adresses etc.

Flash doesn't need to be refreshed. There is a code and it isn't erased after shut down.

Vinoth Ramalingam said:

Where is the C code we have written stored RAM or Flash?

Flash doesn't store C code. Compiler translates code into instructions MCU can understand. MSP doesn't understand what "delay" means but for example this "delay" can be executed by instructions*:

 1. "Copy number 120 to register R12."

 2. "Decrement value in R12 register."

 3. "If value in R12 equals 0, jump next instruction."

 4. "Jump to instruction number 2."

 5.  .... (next instruction). 

*I don't say "delay" is executed exactly in this way. MCUs of other brands have other instruction sets, different compilers can translate functions in different way etc.

Anyway, suppose that:

- copying number to register requires 2 cycles,

- decrementing value in register requires 1 cycle,

- jumping next instruction if value in register is 0 requires 3 cycles if jumping or 1 cycle if not,

- jumping from instruction number 4 to instruction number 2 requires 4 cycels,

then you can count number of cycles you delay is equal: 2+1*120+1*(120-1)+4*(120-1)+3=720.

-----------

Ok, you want to use delay function mentioned above, but it is possible there is a variable in R12 register that will be lost if we write "120" there. It's no problem because we have got a RAM. We can write current R12 register value in RAM and load it back after "delay".  It is related to stack but I wouldn't describe it  here.

Vinoth Ramalingam said:

Flash is program memory which executes our program right?

Flash doesn't execute anything. There is a much more components in MSP. Please check the User's Guide and other files.

Best regards,

Mikolaj

Vinoth Ramalingam said:

I been reading mazidi book about embedded

That is a totally inadequate description!

There are several books with authors named "mazidi" - which one are you talking about?!

This one, perhaps: http://www.8052.com/forum/read/175610 ?

Curt Carpenter said:

The majority of your C code will be stored in flash

Wrong.

As  Mikolaj Filar has already said, none of your 'C' code is stored anywhere in the microcontroller!

Forgive me, but our friend here is wondering what a stack is for, and you're splitting hairs?  Certainly a derivative of his C code is in the microcontroller.   You know that.

So while I wouldn't call your comment Wrong, I do think I'd call it "Not very helpful."  

And the object is to try to be helpful, isn't it?

I do understand C code code will converted to assembly code then to binary code . I just wanted to know where those binary will be placed? I believe the answer is FLASH. 

Re STACK . Does stack store address during execution or before? Stack itself is a section of RAM no? It stores address of RAM? 

8051 and embedded Systems bu mohammed mazidi 

Mikolaj Filar said:

I wrote it to avoid misunderstanding in the future.

Much Appreciated . 

I read this document about STACK . It was helpful . http://eleceng.dit.ie/frank/msp430/msp430.pdf . Incase anyone need it . 

I have another doubt. 

The function of Program counter is to point to the next instruction to be executed right?

Main()

{

int a=1,ba;

ba=ba+1;

txuart();

.......

}

void txuart()

{

...

}

PC keeps point pointing to next instruction. After int ba addition is executed . It points to txuart() subroutine. When it occurs next instruction is stored on the stack and it goes to subroutine. I just want to know does PC know the address of subroutine?? This part i want to know . 

I know after finishing subroutine when RET instruction occurs . Microcontroller pops the address from the STACK to PC and keeps executing . I just want to know the middlepart how PC knows subroutine address... 

Thanks to all the guys who helped me here about STACK esp Curt Carpenter and  Mikolaj Filar

Vinoth Ramalingam said:

The function of Program counter is to point to the next instruction to be executed right?

Yes.

Vinoth Ramalingam said:

When it occurs next instruction is stored on the stack and it goes to subroutine.

Adrdess of the next instruction, of course.

Vinoth Ramalingam said:

I just want to know does PC know the address of subroutine?? This part i want to know .

PC doesn't know anything beside it contains :P Compiller knows this address and it's enough. I'm not brave enough to go lower than assemler, but I can take a guess.

Maybe CALL instruction is executed by 2 commands: "PUSH PC onto @SP"  and "JMP to subroutine addresss". I don't know. You can debug these 2 ways to entering the routine and count number of cycles.

Maybe there is any special component which load the adress to PC?

I wish to know where data segment is implemented? Is it in RAM or ROM/Flash? 

Our local variables are stored in stack which is implemented in RAM . 

static , global variables are stored in data segmented is it implemnted in RAM? Is it so ? If will it lose contents when power is turned off?

Heap is implemented in RAM or Flash?

Thanks again . How do you find these documents . I keep searching in TI forum . I dont find any relevant documents . Any searching tips?

Regards

Vinoth

Some documents you can find here: http://www.ti.com/mcu/docs/mcuprodtechdoc.tsp?sectionId=95&viewType=mostuseful&tabId=1201&rootFamilyId=4&familyId=342&docCategoryId=2&docCategoryId=1&docCategoryId=6&docCategoryId=10&docCategoryId=11&docCategoryId=9&docCategoryId=3&docCategoryId=5

Other sheets can be located on pages with MSP devices.

You can find something on this forum or on other pages.

And probably there is a lot of interesting documents hidden in abyss of hell you will never find.

Best regards,

Mikolaj