ReAl

Questions about differences between new “A-version” of AVR mirocontrollers and their predecessors often are found in site log. People look for “what is the difference between atmega48p and atmega48pa” or “atmega8a and atmega8 programming distinction”.

The “microcontroller programming” sentence may have different meanings.

If “programming” means “writing and compiling a program” you should examine datasheets for given microcontrollers and Migration Notes page. As for program writing there is no difference in most cases. AVR523: Migration from ATmega8 to ATmega8A says:

The ATmega8A is a functionally identical, drop-in replacement for the ATmega8. All devices are subject to the same qualification process and same set of production tests, but as the manufacturing process is not the same some electrical characteristics differ.

The next text shows that only electrical characteristics differ indeed. ATmega8A has lower consumption current and works in VCC and frequency range that was covered by both ATmega8 and ATmega8L.

Be careful.
In some cases, for example for ATtiny2313 and ATtiny2313A we have the same text at the top of the application note but there are much more differences. ATtiny2313A has more capabilities and more registers. An ATtiny2313-oriented program “must” work right in ATtiny2313A because for compatibility reason all new capabilities are disabled by default after the microcontroller reset. Anyway it is worth to examine a new microcontroller datasheet in order to refine your program.
More detailed see in another post.

It is quite easy if “programming” means program loading into the microcontroller flash memory.

“A” and “not-A” mirocontrollers have not any differences for programming device. They have the same fuse set and the same signature so avreal can’t distinguish between them. That why avreal displays all posible device names for given signature both in supported device list and in diagnostic messages:

Device connected, tiny2313|tiny2313A detected.