[Coco] Dual UART with FIFO Card for the CoCo

[Gene Heskett]

On Sunday 13 June 2010, sales at gimechip.com wrote:
>Gene,
>If the Duart Pack is used in a multi-pak, and the disk controller placed
> in a different slot, it wouldn't interfere with the RTC inside of the
> disk controller. Since I used the SCS* signal, the duart pak would only
> be active when it's slot has scs* directed to it. Any pack that doesn't
> need $FF50-$FF5F could still be plugged into the duart packs feedthru
> connector.

Hmmm.  You are aware, and I don't think this effects SCS steering, that many 
of us have solved the IRQ latency problems by jumpering the pin 8's of all 4 
sockets in the mpi together, and removing 3 of the 4 pullup R's?  This 
bypasses the IRQ logic in the slot selector so any IRQ from any pack gets 
through to the cpu instantly.  Then by setting the priority byte in the 
driver, os9 can find the src of the IRQ and service it pretty fast.  In my 
testing, 15 u-secs was the average response time except when all IRQ's were 
locked out while the old B&B clock chip was being read each minute, and that 
usually cost about 140 u-secs.  No more missed characters when downloading!

>I will probably do another design using a quad uart chip and I can allow
>alternate mapping schemes such as the $FF1x or $FF3x area which is
> available on the CoCo3 (but not on the CoCo 1 or 2). If I do a quad pack,
> I will probably map them into 16 bytes and include a "switch" so that you
> switch in the first set of 2 or the second set of 2 uarts. I would
> probably also include a SR latch for each of the four UARTS such that
> when one of them generates an IRQ* it sets it's corresponding latch - the
> four latch bits will have an input port so that, if needed, the coco
> could decide which of the four uarts generated the IRQ*. These are just
> some ideas. I suppose I could actually map all four UARTS into the same 8
> bytes with a "switch" to select which of the foure uarts occupies the
> memory space... these are just some thoughts, but if you think it's worth
> looking into, I'll go to work on it. I am having fun with all of this :-)
>Since my Doctor has yet to clear me to go back to work, designing this
> stuff keeps me from going bonkers.

Chuckle, BTDT.  And you are doing the sort of things I did out of necessity 
2 decades or more ago when I was working in broadcast engineering.  Yes, I 
had a blast at the time.  I enjoyed the looks of other faces when something 
I did with very few resources, worked, and worked reliably.

I wrote the program in B09 and made up a bit of cabling to plug into a GVG 
300-3A/B production video switcher so I could use a coco 2 & a couple of 
floppies, running os9 level 1v2 as a personality storage device, doing the 
same job as an accessory GVG sold for $20,000 called an EDISK, except mine 
gave the tech dirs english language names for their files, and was 4x faster 
than the GVG gizmo.  Used it for 16 years, till we had to get a newer 
switcher.  At which point they gave me that computer.

Now I am 75, and I was going to go help the next door neighbor get the paper 
on his new garage roof, and with the temps and the humidity both above 90, I 
simply didn't have what it took to get up on the roof and give him a hand 
today, the heat about wiped me out.  So I went out to TSC and got a stick of 
1/4" rod, a rat trap, 3 nylock 1/4" nuts & some washers, cut it about 7": 
long, threaded both ends and rigged the washers to cover the augered out 
holes in the sheet metal on my MTD chippers big stick input chute, welded 
those in place, took the rat trap apart to get one of the springs to hold 
the flapper in the chute entrance closed, re-welded the lower lip where it 
had broken away from the knives hitting the wood its chopping up, and put it 
all back together.  It should be good for another 20 years now even if I'm 
not.

If I can be a little nosy, and I'm assuming that you are a bit (30 years 
maybe) younger, do you care to share why the Doc's have you on the shelf?

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
A journey of a thousand miles begins with a cash advance.