Register Descriptions _________________________________________________________________________ | X - 16 bit index register | | Y - 16 bit index register | | U - 16 bit user-stack pointer | | S - 16 bit system-stack pointer | | PC - 16 bit program counter register | |*V - 16 bit variable register (inter-register instructions only) | |*0 - 8/16 bit zero register (inter-register instructions only) | |-------------------------------------------------------------------------| | A - 8 bit accumulator | | | B - 8 bit accumulator | Accumulator structure map: | |*E - 8 bit accumulator | ----- ----- ----- ----- | |*F - 8 bit accumulator | | A | B | E | F | | | D - 16 bit concatenated reg.(A B) | -----------+----------- | |*W - 16 bit concatenated reg.(E F) | | D | W | | |*Q - 32 bit concatenated reg.(D W) | ----------------------- | |------------------------------------| | Q | | |*MD - 8 bit mode/error register | ----------------------- | | CC - 8 bit condition code register | bit 31 24 15 8 0 | | DP - 8 bit direct page register | | ------------------------------------------------------------------------- * Indicates new registers in 6309 CPU. Push/Pull Order of Stack Pull order Push/Pull Post byte | ------------------------------- \|/ | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | ' ------------------------------- CC | | | | | | | |____CCr A\ | | | | | | |________A B/ D\ Q | | | | | |____________B E\ W/ | | | | |________________DPr F/ | | | |____________________X DP | | |________________________Y X-hi | |____________________________S/U X-low |________________________________PC Y-hi Y-low U/S-hi U/S-low PC-hi PC-low . /|\ | Push order Condition Code Register ------------------------------- | E | F | H | I | N | Z | V | C | ------------------------------- Entire flag____| | | | | | | |____Carry flag FIRQ mask________| | | | | |________Overflow Half carry____________| | | |____________Zero IRQ mask________________| |________________Negative The PSH(s,u) and PUL(s,u) instructions require one additional cycle for each byte pushed or pulled. From: HD63B09EP Technical Reference Guide By Chet Simpson and Alan DeKok