[Coco] XPander-Coco lives!
zippster278 at gmail.com
Wed May 25 08:47:37 EDT 2016
In trying to get one of these supervisor circuits to work in this application, I’ve definitely
discovered that some CoCos are much more sensitive to having the reset circuit monkeyed
with than others.
Most seemed to work ok, but I had a couple of machines here that would’t play nice with either
totem-pole or open-drain supervisors, resulting in continual resets (on some machines).
Not wanting to dig into this any further, I’ve settled on a 10uF cap between reset and ground
to extend reset instead of the supervisor. This gives good reliability with all the machines I
have here that I’ve tested so far, though a press of the reset button is sometimes needed depending
on the machine or types of carts installed after power on. Not a big deal I suppose, though I
was trying to eliminate needing to do that with the supervisor.
Anyway, they are working well enough that I’m sending one to John Strong so he can design a case. :)
> On May 1, 2016, at 7:34 PM, RETRO Innovations <go4retro at go4retro.com> wrote:
> On 5/1/2016 7:30 PM, Zippster wrote:
>> I’ll look into an open drain part, the MAX811 was just what I had on hand patching up the boards.
>> - Ed
>>> On May 1, 2016, at 7:25 PM, RETRO Innovations <go4retro at go4retro.com> wrote:
>>> On 5/1/2016 6:13 PM, Zippster wrote:
>>>> That’s a good point I didn’t give much thought to. I know the reset switch works ok,
>>>> but that doesn’t mean something else would.
>>>> Since we’re working with a CPLD in the mix on these boards, I guess the reset
>>>> signal to the cart ports could be routed through it, and used to toggle !MR on the MAX811.
>>> I'd instead recommend an open drain supervisor, which are plentiful. They work the same as the MAX811, but the RESET output is open drain.
>>> Coco mailing list
>>> Coco at maltedmedia.com
> I put the following in my cart to buy:
> MIC803, which seems much cheaper than the MAX811 ($.22 versus $2.10 @100s)
> I chose a 4.38 device, but it appears MIC offers a ton of threshold voltages.
> RETRO Innovations, Contemporary Gear for Classic Systems
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> Coco at maltedmedia.com
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