[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: COP

Bryan Parkoff <BParkoff@satx.rr.com> wrote:

>     It is COP instruction that uses secondary microprocessor with the range
> $00-$7F.  I don't understand what it means.  Can you please give me an
> example of code how to use COP instruction.  Thanks...

The COP instruction was intended to be used with a secondary processor
(such as a floating point coprocessor), but no such device was ever
created.  Half of its operand values were reserved for this purpose.

The theory is that a coprocessor would be monitoring the opcodes fetched
by the 65816, would recognise the COP opcode and decode the operand byte
to select the desired operation.  It would probably need support in the
COP interrupt handler, e.g. by polling an I/O location to determine if
the operation was complete.

The other half of the COP operand values have been used in software on
the IIgs (for the ORCA language debugging tools, if I remember right).

-- 
David Empson
dempson@actrix.gen.nz