From: Hársfalvi Levente (levente_at_terrasoft.hu)
Date: 2003-09-17 12:52:33
Hi!
> While I don't understand what exactly he meant, I guess that this is the
> cause why I don't get any interrupts on my AVR. From its datasheet I
> learned that it has Schmitt-trigger input.
Neither did I fully understand the situation, I just noticed that it
received no interrupts after I changed the microcontroller ;-). I suspect,
the Schmitt-trigger input will notice the level drop (since the signal level
on the POTX/Y lines is always close to 0v -- remember, the input voltage
threshold value of the SID inputs is 0.8v and not Vcc/2), but probably won't
notice the rise. A simple TTL input will switch both forth and back at
around 0.8~1V, but the Schmitt-trigger won't (without a larger voltage
swing) as it has hysteresis.
> Are there any other options?
Use the onboard comparitor of the AVR to trigger an interrupt at whatever
voltage level you set ;-). I'd at least do this. The comparitor has no
hysteresis (as I remember), and you can also set the trigger level by a
simple trimmer potmeter or a fixed voltage divider.
[Marko]
> PS: What is the smallest AVR that has an SPI bus?
I seem to remember a "small" (28-pin) AtMega as the smallest one.
> For instance, the 2313,
> which would otherwise be up to the task, has it only for programming purposes.
Yep :-(
> I believe, however, that you could use bit-banging on the 2313 like Levente
> did on the PIC. On the PS/2 interface you even have the advantage over
> RS-232 that the clock is driven by the "computer", isn't it?
No, it's the other way (if it was that simple, I could have as well done it
on the 16c84 by bit-banging ;-) ). The clock is generated by the device, and
it's pretty fast. By itself, it could be done by bit-banging, but I guess
it's almost impossible to run it simultaneously with the also time-sensitive
1351 emulation task.
Best regards,
L.
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