Search found 7 matches

by NekadZut
Mon Aug 14, 2017 3:37 pm
Forum: Newbie Help Center
Topic: JSR
Replies: 18
Views: 4283

JSR

Do the JSRs in 6502 assembly set the PC to a function's address or the address of a function pointed to in a table high in memory? Like are the two bytes after the JSR the next address the PC needs to be for the function to begin or no? I've learned in assembly and BASIC functions typically declared...
by NekadZut
Wed Aug 09, 2017 6:32 am
Forum: Newbie Help Center
Topic: Expected Memory Values
Replies: 5
Views: 1791

Re: Expected Memory Values

Oh, I'm boosted.

Sorry for that question then

I swear I know CS :lol:
by NekadZut
Sun Aug 06, 2017 3:12 pm
Forum: Newbie Help Center
Topic: Expected Memory Values
Replies: 5
Views: 1791

Expected Memory Values

Other than I/O ports for PPU, vectors, service routines, and program code, should there be any specific values saved in memory? Looking at the iNES rom for Super Mario Brothers, there are the following instructions after the header: ... LDA $2020 ; contents of A now 0x00 BPL FB ; branch is not taken...
by NekadZut
Sat Aug 05, 2017 9:18 am
Forum: Newbie Help Center
Topic: Interrupt Service Routine
Replies: 13
Views: 3624

Re: Interrupt Service Routine

Oh, I see. So whenever the NES is turned on or reset, this interrupt will occur and would set PC to the start of the ROM which is where this code would be supplied.
by NekadZut
Sat Aug 05, 2017 8:06 am
Forum: Newbie Help Center
Topic: Interrupt Service Routine
Replies: 13
Views: 3624

Re: Interrupt Service Routine

Why doesn't this reset/init code have an RTI or JMP to get the PC to the start of the cartridge ROM?
by NekadZut
Fri Aug 04, 2017 7:13 pm
Forum: Newbie Help Center
Topic: Interrupt Service Routine
Replies: 13
Views: 3624

Re: Interrupt Service Routine

Is there not some standard interrupt service routine for the three interrupts on the NES, or do I just write some 6502 assembly service routine and believe?
by NekadZut
Fri Aug 04, 2017 4:39 pm
Forum: Newbie Help Center
Topic: Interrupt Service Routine
Replies: 13
Views: 3624

Interrupt Service Routine

So I understand that an interrupt vector is an address to some area of memory which contains code to acknowledge and handle an interrupt, but exactly what address is stored in little endian at 0xFFFE and 0xFFFF and what does that point to?

Thanks