[Coco] Coco 4

[jdaggett at gate.net]

The 68x09 with internal clock is better suited for DMA operations. 
With the "E" versions you have to use a psuedo DMA.

The internal clock chip has a DMA pin when taken low suspends the 
processor for 32 cycles. It checks every 32 clock cycles to see if 
DMA is through. On the "E" You have to use the halt or do a cycle 
stealing method. You have to treat teh DMA controller as a 
coprocessor shareing the busses.

james



On 6 Jan 2004 at 11:03, Neil Morrison wrote:

From:           	"Neil Morrison" <neilsmorr at hotpop.com>
To:             	"CoCoList for Color Computer Enthusiasts" 
<coco at maltedmedia.com>
Subject:        	Re: [Coco] Coco 4
Date sent:      	Tue, 6 Jan 2004 11:03:40 -0800
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> 
> I hadn't even considered DMA. The no-halt design of some controllers
> would be nice however.
> 
> Neil
> 
> ----- Original Message ----- 
> From: <peak at mail.polarcomm.com>
> 
> 
> > The memory of an ISA card would be decoded using coco's CTS
> > line and the I/O using coco's SCS line. If you really want an
> > ISA card adapter for the coco I will see if I can design one
> > at least as far as a schematic diagram. Warning* I wont even
> > attempt using DMA though**. The hardware part of an ISA card
> > adapter for 8-bit ISA cards that dont use DMA should not be a
> > problem. I have been wanting to do this anyway.
> > Note: Many ISA cards need a 14.318Mhz signal.
> > The coco1 and coco2 have this frequency but coco3 does not.
> 
> > Eric
> 
> 
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