Date   : Wed, 29 Apr 2009 23:52:36 +0100
From   : jgh@... (Jonathan Graham Harston)
Subject: Odd behaviour of the STA &****,X command?

"Mark Haysman" wrote:
> If the command is used without the index - IE: STA &FC40 -  the CPU makes
> one write to the memory location as you'd expect, but if you use the X
> index - STA &FC40,X -  it seems to perform a read immediately afterwards
 
I think you're supposed to avoid using indexed instructions to
access I/O ports precisesly because they perform actions that are
appropriate to memory but may not be appropriate to I/O devices.
 
-- 
J.G.Harston - jgh@...                - mdfs.net/User/JGH
RISC OS Internationalisation - http://mdfs.net/Software/RISCOS