[sdiy] uC with mul

[Theo]

That's a rather large ROM.
Considering the added costs it might be cheaper to migrate to a
MegaAVR with mult or move to a ARM part right away.

Theo


From: Jim Patchell <patchell at silcom.com>

>      Here is a thought for doing an 8x8 multiply...use a look up table.
> If you use a 128Kx8 ROM, you can put a look up table in it to make an
> 8x8=16bit multiplier.  All you need are two 8 bit registers, and then
> use one of the address lines to access the MSB and LSB parts of the
results.
>
>    Anyway, just a thought.
>
>    -Jim
>
> Scott Gravenhorst wrote:
>
> > I did quite a bit of assembly programming with a MC6800
> > MPU (not 68K !) which has no mult instruction at all.
> > There are cases where you need to multiply a variable
> > number by a constant.  In these cases, a short sequence
> > of shifts and adds does the trick and can be faster than
> > using a generic multiply subroutine.  So if you are
> > stuck with a no-mult mcu, or if you have 8x8 and need
> > 8x16 or 16x16, this technique can be useful as well.
> > Much depends on how fast the builtin 8x8 is.
> >
> >>> -----Original Message-----
> >>> From: ext John Loffink [mailto:jloffink at austin.rr.com]
> >>> Sent: 30. December 2001 17:08
> >>> To: Byron G. Jacquot; synth-diy at dropmix.xs4all.nl
> >>> Subject: RE: [sdiy] uC with mul
> >>>
> >>>
> >>> The multiply cycle on the 68HC16 is 8 cycles.  Other micros
> >>> do have the
> >>> multiply instruction, usually multi cycle instructions.
> >>> These might be
> >>> good enough depending on your application, particularly for low
> >>> frequency stuff like note generation, envelopes, LFOs,
> >>> control sources,
> >>> etc., but for anything related to analog synthesis it's
> >>> generally better
> >>> to have 12-16 bits of resolution to avoid stair-stepping.
> >>>
> >>> John Loffink
> >>> jloffink at austin.rr.com
> >>>
> >>> -----Original Message-----
> >>> From: owner-synth-diy at dropmix.xs4all.nl
> >>> [mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of Byron
> >>> G. Jacquot
> >>> Sent: Saturday, December 29, 2001 10:29 PM
> >>> To: synth-diy at dropmix.xs4all.nl
> >>> Subject: RE: [sdiy] uC with mul
> >>>
> >>>> Motorola M68HC16 microcontroller series has a 16 bit
> >>>> multiplier/accumulator.
> >>>
> >>> The "little brother" 68HC11 could also do 8*8 multiply, and
> >>> (IIRC) 16/8
> >>> division.  They were both kinda slow.  I think a multiply took 12
> >>> cycles,
> >>> and the divide something amazing like 42.
> >>>
> >>> Byron Jacquot
> >>>
> >
> > =========================================================
> > - Government: The other religion.
> > - The media's credibility should always be questioned.
> > - Lambs who lie down with lions are lunch.
> >
> > -- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
> > -- Linux Rex         | RedWebMail by RedStarWare
> > -- FatMan: home1.GTE.NET/res0658s/TekLab_FatMan_WebSite/index.html
> >
> >
> >
> >
> >
>