Re: userport: C64, Plus4, others?

From: Jim Brain <>
Date: Fri, 09 Mar 2012 11:47:30 -0600
Message-ID: <>
On 3/8/2012 3:33 AM, Gábor Lénárt wrote:
> What HiZ is? I guess it's high impedance, am I right? As being 
> Hungarian I am not sure about the English notion of things sometimes, 
> sorry about it. 
Yes, it's high impedance.  It allows multiple items to exist on a bus.  
Bil's response gives more detail, and he's better to respond on this 
topic than I.
> Yes, but my idea that always the C64 is the one who must start a 
> transfer regardless of the data direction (read/write). uC won't 
> respond by its own, but C64 requires both of the read/write signaling 
> with another line (maybe PA2 on userport or something like that). So 
> the C64 sets the direction up on CIA, and uC is signaled about the 
> data direction by the C64 so it will know as well about the transfer 
> direction.
That's fine.  In general, you simply have to ensure that both devices 
(64,uC) are not trying to drive the data lines at the same time.
> Maybe, however I would like to use an uC which has the minimal number of
> pins as possible (using more ports on uC means more pins), I mean using a
> DIP version is OK, but I think I have got no skills and tools to solder
> chips which are not DIP.  Also making a board as a "DIY" style would be
> quite hard then (for me at least).  I have some experience to build more
> basic boards/soldering using discrete stuffs and DIP ICs.
The ATMEGA16,162,32,644P are all available in DIP40 format, and 
ATMEG28/48/88/168/328 all are in DIP28 package.  And, using 1 IO port on 
the AVR is fine, as long as you ensure only 1 output on the "bus" at a time.
> Btw, for starting point I'd like to wire some kind of SD socket, with dual
> purpose: uC would "boot" its "firmware" from it (there are boot loaders for
> AVR like this afaik) and also it can be used to read/write data sent/read by
> C64 too (yes, I know, SD2IEC and like are "better" because they are "ready"
> and compatible with a stock machine too - since it uses std IEC bus, but
> also because of this, it can't be as fast, and also note that having the SD
> storage is only a part of the project, and not even the primary goal). It's
> a bit like however as IDE64; it's also not compatible at hw level (it does
> not using IEC) the compatibility is provided with KERNAL modification (on
> DTV it's really easy, no need for additional hardware).
Yes, bootloaders work well for this (the uIEC bootloader can load any 
firmware image, not just sd2iec, so you can use it if desired).  But, 
remember that loading a firmware image on each boot will wear out the 
FLASH area.  It's a large number of cycles, but keep it in mind.


Jim Brain

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Received on 2012-03-09 18:00:17

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