A92: Motorola user's manual
[Prev][Index][Thread]
A92: Motorola user's manual
> Hi,
>
> Does anyone know what the static and dynamic adjectives mean in the
motorola
> M68000 user' s manual ( M68000UM/AD rev 8 ) , section 8-7, table 8-8.
> Thank you,
>
> Mathieu Lacage
When dealing with either hardware or software...static typically means
"fixed/unchanging" and dynamic means "in flux/changing." In your case,
this refers to the source operand of the BIT instructions of the
MC68000.
The "static" case is the unchangeable case...when the source is #<data>
(immediate data). The bit number contained in <data> in part of your
code and is considered fixed...every time that instruction gets executed
it is the same bit affected every time (eg #5 always affects bit number
5).
The "dynamic" case is the alterable case...when the source is Dn (Data
Register Direct). The bit number contained in the Data Register may be
different each time the instruction gets executed.
When the bit number is contained in a data register (dynamic) you will
notice that the execution times are faster. This is because the 68000
doesn't have to load the bit number from memory...its already in an
onboard register. Conversely, when the bit number is part of the coded
instruction #<data> (static), the 68000 has to go to memory and get
#<data> before it can perform the BIT instruction...that takes a little
more time.
Hope that helps...
TTFN - ta ta for now
====================
Keith Kirton
kkirton@acex.com