Re: Question about 65816

From: Stephen Judd (judd_at_merle.acns.nwu.edu)
Date: 1998-07-08 20:34:53

Hi Ruud!

> 1-    The datasheets say the BRK and COP instruction are 2 bytes long when
>       in native mode. Correct?

Yup!

> 2-    (Only if answer for 1 = yes) When I look further the only thing
>       related to this second byte is a byte, called Signature, which is
>       read. The only thing I can imagine of this is that this byte can be
>       used for programmers to find out which BRK or COP has caused the SW-
>       interrupt. correct?

Yup!

> 3-    (Only if answer for 1 = yes) Used in the emulation mode, the BRK
>       instruction only must be 1 byte long. But still PC seems to be
>       increased with 2 after the instruction:

Actually, the 6510 one is also two bytes long.  If you look at the
BRK spec in e.g. the Programmer's Reference Guide, it pushes
PC+2 onto the stack; similarly, if you look at e.g. the source code
for Supermon it subtracts 2 from the PC counter on the stack to
get the correct PC.

> 4-    JML = JuMp Long ($..) but the datasheet says it is "absolute
>       indirect". This means it has to be used like this:
> 
>             JML  ($1234)
> 
>       causing the 65816 to fetch the three bytes from the address
>       $1234..$1236. Correct?

Yup!

Hey, this one was pretty easy -- three Yups and two sentences :)

-Steve
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