There is a genealogy in Motorola microcontroller development that went something like this:

6800 - 6809 - 68000 - Coldfire
|
6802 -> 6502 - 6510
|
6805
|
68HC11 - 68HC12
:
Atmel AVR - ATtiny - ATmega -> (Arduino)

I have loosely included the Atmel AVR because personally I have found that HC11 and AVR programming to be very similar.

 

If you can program 6805, you can program HC11, AVR, MSP430.
(I failed to include 9S08 family in the previous post.)

Personally, if you want to learn ASM programming on any of the above, I would begin with TI MSP430 LaunchPad.

 

I would begin with TI MSP430 LaunchPad

any reference available?

 

I've been away from the basics for so long that my opinions may or may not be relevant. Since Microchip purchased Atmel and the AVR line it is hard to fathom what their long term plans might be. Sometimes a company will purchase a competitor for the purpose of putting it out of business. I can't really tell if that is the case here or not. the best advice would be to remain flexible and don't invest too much time on any one alternative. You might want to spend time looking at software development tools and programming hardware before selecting a part.

 

any reference available?

Google is your friend:

http://www.ti.com/tool/MSP-EXP430G2ET