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In article <2676@milano.UUCP> baxter@milano.UUCP writes:
>Those of you having CoCo IIIs and some understanding of the hardware
>can do a great service for those of us who don't.  CoCo III promises
>compatibility of peripherals with CoCo II peripherals, presumably
>including floppy disk controllers and modem cards.  It also promises
>1.8 Mhz operation.  Usually faster processors won't work with
>controllers designed for slower machines controllers (Motorola
>supplies different versions of it 6809 family for different clock
>rates); can someone explain why the CoCo III should be an exception?

The CPU chip in the CoCo 3 is a 68B09E,  the B part means it will run
at 2 mhz. Yes in theory the peripheral parts should also be B's to run
at that speed. (ie 68B21 68B50 ). In practice however, most parts will
run at the higher speed, but , they are not garanteed by the manufacturer
to run at that speed under all temperature extremes. For critical aplications
it would probably be best to slow down the I/O on the CoCo 3.

>For BASIC, I suppose that the following strategem might work: run at
>1.8Mhz until I/O is necessary, slow down to .8Mhz, do the I/O, speed
>back up again.  If this was done consistently, I don't understand the
>CoCo III is delivered running at .8Mhz as the default (excuse my
>ignorance if that's not the case... data on the CoCo III is really
>hard to find right now).

The CoCo 3 defaults to 0.8 mhz to be completely compatible with the CoCo 2.
This is in case software was timing via instruction loops, etc.
In a BASIC program you can POKE it into high speed mode. You should POKE it
back for disk I/O though. Reports are that disk I/O will work at fast speed
but it is not reliable.

>Under OS-9, the strategem wouldn't work as well, especially if several
>devices were busy at once.  Reducing OS-9 to running at .8Mhz as the
>least common denominator would make a joke of the 1.8Mhz ability.
>Anybody sane would automatically WANT the 1.8Mhz as the default, so I
>presume that it is under OS-9... so there must be a different
>strategy.

I understand that OS9 Level II does run in fast mode, but slows down for
disk I/O ( the driver automatically does this )


>An aside: was the typeahead problem with OS-9 ever solved (i.e.,
>I can't typeahead while the disks are spinning?

You always could type ahead while the disks were spinning, it was when the
actual data was being transfered that the disk controller HALTS the CPU
on a byte by byte basis, also the interupts are turned off here of necessity.
Since you use the same disk controllers on a CoCo 3, this problem will still
exist. It however, should be MUCH better (if they wrote the code right )
since the keyboard now will generate an interupt! Even if the machine is
HALTed the interupt should get seviced eventually. We will have to wait
for Level II OS9 to find out.


>Ira Baxter            arpanet: baxter@mcc.com
>MCC Corporation       usenet:  ut-sally!im4u!milano!baxter


-- 

               Roger Sanderson
               Electrical Engineering Dept.
               University of Waterloo
	       Waterloo Ontario Canada
               N2L 5E6
   
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