[Coco] OS9 68K, MM/1 software and questions

Joel Ewy jcewy at swbell.net
Wed Dec 30 23:58:07 EST 2015

On 12/30/2015 10:04 PM, Mark McDougall wrote:
> On 31/12/2015 1:34 PM, Joel Ewy wrote:
>> I concur.  It really was a very nice computer in its day.  I also had
>> (and still have) an Amiga 1000, and it compares very favorably with that
>> machine.  The clock speed was better, and the 256-color graphics were
>> sharper than HAM.
> You've got my attention...
Just a few more details off the top of my head.  The CPU is a Signetics 
68070, which has a 68000-compatible core (though not clock timing 
compatible per instruction) with a built-in MMU of sorts and maybe some 
built-in timers and a serial port.  The CPU is clocked at about 15MHz, 
so it's a bit faster than a base-case Amiga 1000 or 500, though it 
doesn't exactly compare cycle-for-cycle.  The video chip is a Signetics 
66470.  It was designed for CD-i systems if I understand correctly, but 
I believe I read that they would have used 2 of them in tandem, for a 16 
bpp display, where the MM/1 just uses one.  The Magnavox CD-i 450 I have 
uses a later, but presumably compatible single video chip.  The MM/1 has 
a Brooktree video DAC that can do 256 colors out of 16M (24-bit 
palette).  The I/O board has 2 8-bit DAC/ADC chips from Analog Devices 
that are used for stereo audio and CoCo joystick.

K-Windows supports the following video modes:

DWSet code    Char Size        Pixels    Colors    Type
00                    80x26           640x208    16 non-interlaced
01                    80x26           640x416    16 interlaced repeat
02                    80x52           640x416    16 interlaced
03                    40x26           320x208    256 non-interlaced
04                    40x26           320x416    256 interlaced repeat
05                    40x52           320x416    256 interlaced
06                    96x30           768x240    16 non-interlaced overscan
07                    96x60           768x480    16 interlaced overscan
08                    48x30           384x240    256 non-interlaced overscan
09                    48x60           384x480    256 interlaced overscan

The video chip, as far as I can tell, does not have a blitter or copper 
like the Amiga, but the faster clock may make up for some of that.  The 
68070 cpu is supposed to have some sort of DMA built-in. I don't think 
K-Windows takes advantage of it, and I don't know if it can be useful in 
moving large chunks of data around in memory for games and whatnot, but 
it would be worth a look.


> Regards,

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