[Coco] [Color Computer] Re: Coco flash cartridge

[James Diffendaffer]

>That's just what Altium Designer came up with for the button. 

That's kinda what I figured.

>I'm actually using one of these...
><http://au.farnell.com/jsp/Electrical/Switches+&+Accessories/OMRON+ELECTRONIC+COMPONENTS/B3F-1000/displayProduct.jsp?sku=176432>
>It should be almost impossible to 'bump'. As it is, the PCB barely
>protrudes
>from the cartridge port, so it needs to be on the outer edge with the
>LED, otherwise there's no hope of access while it's plugged in.

That's ok for a prototype but for production you have to remember that
most people would want to reuse a game cart case if it will fit.  That
probably means some sort of right angle switch or solder pads to
attach a remote switch.  And if you plug it into a multipak interface
you would have to feel around for the button even if the board isn't
in a case if you use that button.

I'd like to use it as part of a coco repack eventually so a remote
button would be in order or a 555 timer chip that trips the reset
automatically if you hold the system reset for several seconds. 
Du-oh!  I should have thought of that to begin with.  I used a circuit
like that for an Amiga ROM switcher.  If I remember right it requires
a couple resistors and a capacitor to set the time interval.
If you google 555 timer you'll get a lot of examples if you want to
check it out.  I suppose you might be able to have a timer in your PLD
as an alternative.

One big advantage to that over a switch is elimination of a possible
static discharge with the user reaches for the reset.  

LOL... don't you just hate scope creep?


>> I'd like to develop some stuff for the board, let me know how much >>it
>> will cost for one. If you can provide the info on the ports ahead
>>of time that would be nice.
>
>
>I'll let you know when we've paid for the panel and I work out how
>much I
>need to charge for the board to break even. All the parts are quite
>cheap
>except for the flash, and since I'm not buying in bulk it'll be the
>killer.
>You may want to purchase a bare board if you can do better on the
>flash?!?
>It's industry-standard TSOP40...

Sadly the flash memory I have isn't... or at least I don't think it is.

>Decoding with A0 means there are 2 addresses within SCS# - ie.
>$FF40/1 and their aliases.

I understood the A0 part... just not familiar with SCS#... haven't
looked at the pinout of the coco cart port for a couple years.  That
should be fine.

> I was planning on starting on the CPLD code sooner rather
>than later, but I can envisage:
>@$0 - Bank Select (8-bits, WO)

Read only is fine... we'll just have to track the page in software. 
Perhaps we can store the current page # on the last address of each
page so a program will know what page it has been launched from.  Then
if a program requires multiple pages it can know which ones it's on as
long as they are consecutive.  Otherwise we'd have to do everything
through a file system that will require time.

>@$1 - Control: WR - Bit0 = 16/32KB, Bit1 = auto-start enable (maybe?)
>RD - Bit0 = Flash RDY/BSY#

Sounds fine to me but I haven't programmed flash chips directly in
years and back then you even needed to manually erase them.
I know that some Flash memory will let you access one block while
another is erased.  Will one bit on the read be sufficient to handle
that or does the standard form factor not allow for this?  

>A jumper on the board sets default auto-start (Absent=auto-start)
>which I'm
>thinking can be overridden in s/w via the Control bit above?!? 
>Haven't thought this through.

This might prove useful if you want to fall back on a standard
cassette system.

>The RESET# switch on the Coco won't reset the bank select register. 
>However,
>the reset button on the cart will, and perhaps will also reset the
>system?!?
>
>How does that sound?

You have to be able to reset until artifact colors are correct without
resetting the bank but you must be able to reset the bank without
turning the machine off.  And since the system will probably die in a
horrible manner if you reset the bank you are better off just
resetting the system along with it.

Sounds good to me Mark.  


>Regards,
>
>-- 
>
>| Mark McDougall | "Electrical Engineers do it
>
>| <http://members.iinet.net.au/~msmcdoug> | with less resistance!"