In message <0043C076.4149@autodesk.com>, ERIC SCHLAEPFER writes >Hello, > >Does anyone know the input and output impedance of each I/O line in PORTB >of a 16F84? I can't find it in the data sheet. I don't think that impedance is very meaningful in this context, which is why it isn't quoted. The AC output impedance is probably highly frequency- and load-dependent, unlike a linear amplifier. I've checked through some of the different manufacturers' data I've got, and can't find any who specify it. You could probably model it for a given set of conditions, if you knew the characteristics of the input/output devices. Inmos used SPICE simulation to characterise the transistors used in the transputer, for instance. I've just looked at the data for a VHF mixer device. This is an analogue chip, and the mixer input impedance varies quite a lot over the design frequency range. Digital devices would be much messier. Leon -- Leon Heller: leon@lfheller.demon.co.uk http://www.lfheller.demon.co.uk Amateur Radio Callsign G1HSM Tel: +44 (0) 118 947 1424 See http://www.lfheller.demon.co.uk/dds.htm for details of my AD9850 DDS system. See " "/diy_dsp.htm for a simple DIY DSP ADSP-2104 system.