PDA

View Full Version : Recommendation for reset IC in Propeller project



ags
08-31-2011, 01:11 AM
I'm designing a board usign the P8X and the WizNET module. I'm running out of I/O pins. Up until now, I've dedicated a Prop I/O pin to reset other components (the WizNET module, registers, etc) at startup. I'd like to reclaim that I/O pin for use in other areas. I've read that without Schmitt trigger input, a simple RC circuit won't likely work. I've searched and see there are a plethora of options (too many to search through). I was wondering if there is a standard way of doing this that is used by people on this forum. One additional complication is that I have both 3.3v and 5v chips that will need to be reset on power up. Luckily, they both have RESn (low reset). Thanks for any suggestions/tips from your experience.

Phil Pilgrim (PhiPi)
08-31-2011, 01:49 AM
Firs of all, will the 5V chips run with their /RST pins held at 3.3V?

-Phil

ags
08-31-2011, 04:57 AM
Firs of all, will the 5V chips run with their /RST pins held at 3.3V?

-Phil

Yes, my apologies, I should have made that clear. I'm using a 74HCT595 part; V(ih) min=2.0v, so 3.3v in to the /RES pin will take the part out of reset state. The WizNet module runs on 3.3v supply so it's also OK.

Phil Pilgrim (PhiPi)
08-31-2011, 05:05 AM
If you enable brownout reset on the Propeller, the /RES pin gets pulled low during power-up. It might be able to sink enough current to reset those other two chips. 'Maybe worth a try!

-Phil