[Coco] The MOOH board (MMU/SPI) for Dragon/CoCo1/2

[Gene Heskett]

On Sunday 18 March 2018 12:25:41 Tormod Volden wrote:

> On Sun, Mar 18, 2018 at 4:46 PM, Gene Heskett wrote:
> > I've seen mention of an SPI interface, and am wondering what is the
> > bandwidth achievable? I am currently running an 11" swing by 54"
> > bed, 70
>
> Hi Gene,
>
> The on-board oscillator is 48 MHz, and the SPI interface has a
> programmable clock divisor (from 2 to 32), it can also use the
> computer E clock as a source to go slower (SD cards are initialized at
> slow speed). At high speed settings a new byte is clocked in faster
> than the 6809 is able to read from the port address, even when
> "over-clocked".
>
> The block read routine in FUZIX does (with divisor = 4):
>  lda <SPIDATA
>  ldb <SPIDATA
>  std ,x++
> in an unrolled loop.
>
> I don't remember if I did the cycle math for 6309 TFM transfers, but I
> think it also will be CPU-limited.
>
> I chose ~48 MHz because it is fast enough to saturate the CPU, and
> with the divisor goes down to where the E clock-derived speeds take
> over.

IOW, nominally 1/2000 of the pi's top speeds. That puts the differences 
in context. Still, it might be fast enough to run a tool changer, but we 
already have that code, so the major problem is in adapting or building 
the hardware, either for a carousel, or a geneva driven chain of tool 
pockets. And while I have made a half hearted start, I keep running out 
of drawbar actuator ideas, and real estate to make it all fit without 
getting in the machines way. The drawbar needs at least 60 lb/ft of 
torque, which the spindle drive doesn't have even if the drawbolt is 
locked and the spindle motor run in the correct direction. Such torque 
needs will likely strip the teeth off the 2 speed gear change gears as 
they are plastic in this Chinese mill. So the spindle quill would need 
to be pinned to lock, and the top of the bolt driven by a separate 
mechanism.  That complicates things considerably.  Sigh...

> Regards,
> Tormod



-- 
Cheers, Gene Heskett
--
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