[Coco] Geranium Diode Upgrade

[jdaggett at gate.net]

Chuck

To me it seems more a hardware fix to correct a bug in the ACIA pack more 
than a GIME fix. As it was only the ACIA pack that seemed to have issues. 
Although the GIME chip did have some quirks with it in the 1986 production 
run, the 1987 part from VLSI was more stable. There were timing issues 
with some of the 1986 GIME chips. Especially in the video section. The 
IDMA timings are very critical and have little margin for error when the Coco 
3 is ran at 1.78 MHz buss rate.

james 


On 10 Jul 2008 at 17:16, Chuck Youse wrote:

> On Thu, 2008-07-10 at 17:09 -0400, Chuck Youse wrote:
> > On Thu, 2008-07-10 at 14:03 -0700, Mike 0rtloff wrote:
> > 
> > > The ACIAPAK driver requires this interrupt signal 
> > > to operate properly, although the MODPAK driver 
> > > does not. The signal in the CoC03 is routed 
> > > througi1 the GIME chip, which every so often does 
> > > not pass it to the CPU. 
> > 
> > Am I reading this right when I infer that the GIME has some sort of
> > bug w/r/t its interrupt 'controller'?  That would be a rather nasty
> > flaw ..
> > 
> > C.
> 
> Hmm, ok, after looking at the schematic of the Coco 3 my concerns have
> increased.  This modification bridges CART* straight to the IRQ* pin
> of the processor, bypassing the GIME entirely.  
> 
> Any ideas what the actual GIME bug was?  Anyone?
> 
> C.
> 
> 
> 
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