> Hi you Atmel types: > > Have an application we have to convert to a PIC in the very near future, > and am trying to figure out how the circuit we have been given is working. > > Two Questions: > Port 3, Pin 6, setup for input--does it have an internal pull up resistor, > and if so, what is the value (approximately)? > > Port #, Pin 7, setup for output--is this an open collector/drain type > driver? Pin has a pull up to 3.0 volts for level shifting from the 4.5V > rail--and this is the only way I can figure that it would work. > > Thanks, > Kelly > > > William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems > & San Diego, California, USA > P3.6 does not physically exist as a port pin, it is used for reading the output of the analog comparator. Treat it like a digital input, no need to worry about pull ups or anything. P#.7? Looking at my keyboard I think you mean P3.7 This is a standard I/O pin with weak internal pull up. As a rule assume this pullup is approx 30k (calculated from DC specs) but remember that it is non-linear. Sounds like in your circuit the external pullup resistor (<30k?) overrides this and gives you a rough 3V output. The only two open drain pins are P1.0 and P1.1 Changing to a PIC? Good - do it - but only if it offers you some advantages for your application. You might look at the AVR AT90S2313. Drop in replacement for the AT89C2051 except for opposite reset polarity. Brent Brown Electronic Design Solutions 16 English Street Hamilton, New Zealand Ph/fax: +64 7 849 0069 Mobile: 025 334 069 eMail: brent.brown@clear.net.nz