65816 Timing

Albert · Post by **Albert** » Thu May 18, 2006 9:57 am

Hi, I've a question related to the GTE 65816 Document. Acording to Anomie's Timing doc, internal operation always take 6 master cycles, do writting operantions count as this kind of instructions (Before you flame me, in an x86 cpu when it writes to the bus it just sends the order and forgets about it, not like a read where it has to wait for the value, so that's why I ask and please correct me if I'm wrong). And what exactly are internal operations? in GTE doc I mean, are those only the ones that say IO or there's another requirement for a cycle to be IO?

Thanks for taking the time to actually answer.

mozz · Post by **mozz** » Wed May 24, 2006 7:01 am

Every CPU cycle performs zero or one memory accesses (read or write). "Internal Operation" means it is busy doing something, but it isn't a read or write. Those CPU cycles are always 6 master cycles long.

For a "Read" or "Write" cycle, the length of the CPU cycle might be 6, 8 or 12 master cycles, depending on what address was written, and whether a certain bit of a certain register, was enabled (which allows faster accesses--6 instead of 8--to some address ranges). If I remember correctly, 12 is only used for a small range of addresses that map to some internal registers.

Edit: the W65C816S data sheet has a long table that describes what the 65816 does during each CPU cycle. If it says "IO", that is an Internal Operation cycle. The W65C816S is almost identical to the 65816 core used in the SNES. I don't believe there are any known timing differences between the two chips.[/url]

magno · Post by **magno** » Tue Aug 15, 2006 12:29 pm

Would you mind pointing me to that GTE 65816 document you talk about? I have been "googling" but I can't find the GTE webpage, neither that datasheet you refer to..

creaothceann · Post by **creaothceann** » Tue Aug 15, 2006 6:21 pm

He already posted the link. Set your board skin to the default phpBB one to see it.

mozz · Post by **mozz** » Tue Aug 15, 2006 8:29 pm

Your "googling" might need practice too --- if you put "W65C816S" into Google, the first result is the manufacturer's page for that chip and it has a link to the datasheet about half way down.

magno · Post by **magno** » Wed Aug 16, 2006 6:07 pm

creaothceann wrote:He already posted the link. Set your board skin to the default phpBB one to see it.

I guess you meant "Board Style", not "Board Skin", but I can see why I should see one link with one style and not with another... Whatever, if the link you said I should see is that mozz posted, I am not interested on it, as that is the official WESTERN DIGITAL one, and I want GTE's. Thanks anyway.

mozz wrote:Your "googling" might need practice too --- if you put "W65C816S" into Google, the first result is the manufacturer's page for that chip and it has a link to the datasheet about half way down.

I don't think my "googling" needs practice, but my english expression maybe does... I think I asked CLEARLY for GTE's 65816 datasheet, not WDC's.
To be precise, I want the datasheet of part G65SC816.
To be more precise, I want the datasheet Albert spoke about in this line:

Hi, I've a question related to the GTE 65816 Document.

Thank you both, but if anyone else could help, I really would appreciate it.

DMV27 · Post by **DMV27** » Thu Aug 17, 2006 9:51 pm

Here is the GTE 65816 datasheet with the many corrections that I have added to it.

http://rapidshare.de/files/29783722/65c816.zip

Post by **pagefault** » Thu Aug 17, 2006 10:56 pm

Thanks! I will update my docs.

magno · Post by **magno** » Fri Aug 18, 2006 8:57 pm

Thank you very much, DMV27! That's what I was looking for!