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. Message was sent through the cbm-hackers mailing list
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