USR function
Posted: Sun Jun 12, 2016 4:00 pm
Hi, I'm going through "Spectrum Machine Language for Begginers" And its going fairly well but at the beginning I was baffled by the line "don't forget that the function of "USR" is to execute a machine language subroutine", but this was the first time USR was mentioned in the book! Can someone explain what it is and why is it the value of the bc register pair at the end of running a program? I can't find anything about it with google but my guess is its a subroutine stored in ROM/RAM??? that executes Machine code instructions.
Thanks
Thanks