About RA4 - Open-collector Output, Schmitt trigger Input 1 - It can't source *ANYTHING* itself 2 - It can sink quite a bit, and it has in-built protection diodes to drain off excess voltage (at the level you would use). As you have suggested the solution for your problem is to make the pin an output and 'pull up' its output with a resistor from +9V. The +9V either goes to the 4017 when the PIC +5V output is Hi, or is pulled into RA4 when it is Lo (thus providing a level shifted output, exactly what RA4 was designed to do). If it doesn't reliably clock then add a 1K between the 4017 and the pull up so that the PIC will always win a struggle to sink the voltage. You should design for a minimum 1mA @ 9V to trigger the 4017, so from R=V/I = 9/0.001 = 9K, use 4K7 for a 'more than strong enough' signal. Bye. -----Original Message----- From: Allen Mahurin [mailto:wild_wire@YAHOO.COM] Sent: Thursday, 25 October 2001 6:35 To: PICLIST@MITVMA.MIT.EDU Subject: [PIC]: Need advice on using the Open-collector output I'm using a 16F84, so you guessed it ... I'm talking about RA4. It's the only unused pin I have for a project, and I'm wanting to clock a decade counter 4017 with it. I know it can't source much, so I want it to sink current (trigger the counter on a negative going pulse). Anyway, the question is: The PIC runs on 5V, while the 4017 runs on 9V. If I tie the clock input of the 4017 to 9V through a 4.7k or 10k resistor, and use the PIN input to pull it low (tied between the resistor and 4017 input), will this hurt the PIC? I know it would be sinking current, and it would be low, which is OK. But will putting 9V into the open-collector output cause problems? I'd like to see if anyone knows from experience before I kill a good chip. :) If this won't work, does anyone have any other low-parts count alternatives? Thanks, ATM __________________________________________________ Do You Yahoo!? Make a great connection at Yahoo! Personals. http://personals.yahoo.com -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads