| ??? 10/05/07 20:25 Modified: 10/05/07 20:35 Read: times |
#145496 - there are a number of forces at work here Responding to: ???'s previous message |
Jan Waclawek said:
... to discover what was your exact setup. Yes, and I wish I could help more with that, but I've torn this setup apart and rebuilt it several times, removing and substituting features just to see whether there was a combination that would behave properly. OK, so now I know it was on THAT breadboard. That leaves VCC and GND out of question. Yes, I seldom wire-wrap circuits on other sorts of boards, unless there's a specific reason. However, if you still have that setup on hand, I would like to ask you to wire up the trigger to reset (and set to rising edge), and try to look at the RAM's chipselect and/or perhaps VCC. Also, it would be good to know where exactly is the threshold of the '1232 you used - do you have a regulated power supply to play with VCC while watching reset? I've not preserved it, and used it for something else, where, BTW, it seems to work OK with the RC reset. Don't try to conclude anything from that. It's COMPLETELY different! I could perhaps try a similar setup on Monday, but I don't have a DS89C420, only a DS89C450. Where external resources are concerned, there isn't a dime's worth of difference between the '420 and the '450 aside from the fact that IAP actually is supposed to work on the 'C430..'C450. I don't think any of the external behaviors are different. I would stick to the RC reset, at least initially. These DALLAS parts have built-in Vcc monitoring and should work just fine with the built-in reset circuit. They also have an RC oscillator that runs until the crystal oscillator is stabile. Jan There were a couple of reasons why I was using the '420, aside from the fact I had a handful of them lying about and had used '420's a few times already with considerable success. First of all, the '420's I used were OLD, meaning they were of the 50 MHz variety with FLASH that wouldn't work at that speed. Secondly, I had hoped to exploit that fact, though I'm stalled now. As you probably know, the '420..'450 are one-clockers with no way to start up as anything other than one-clockers. That means that their default external memory cycle is four clock ticks long rather than twelve, which reduces the available time for external memory fetches. There are other SFR-controlled timngs and features that bear watching as well. I figured I could play with these using the '420 and external combined-code-and-data memory. It's nice to read things in the datasheet/user-manual. It's much nicer, and more convincing, too, if they're on the instruments in front of you. BTW, while I did see BBRAM corruption when using the RC reset rather than the DS1232, I saw no evidence of activity on the BBRAM control signals during power-on cycle reset. I only saw it during the early part of Vcc decay. RE |
