Talk:RSSB

Am I right in thinking that the detailed sequence goes as if it were implemented as follows?

- Subtract contents of accumulator from contents of specified address, placing result in accumulator.

- Move contents of accumulator to specified address.

The reason I ask is that this is subtly different from:-

- Subtract contents of accumulator from contents of specified address, placing result in specified address.

- Move contents of specified address to accumulator.

The difference is, if the specified address is two, it always contains zero, but the former approach leaves the accumulator holding minus its previous value while the latter approach leaves the accumulator holding zero. (Similar things can happen with the I/O mapping addresses.) So, what is the precise behaviour here?