As stated by others a good scan rate is greater than 50Hz, therefore you should switch digit on a 4 digit display once every 5mS, Normally with a 4MHz clock I set TMR0 on an internal prescalar of divide by 16 and use the overflow interrupt to switch digit. The 16c84 does not have an internal oscillator - it always needs external components, those PIC's which do have an internal oscillator do not need a connection to the external pins - often these pins are dual purpose and are I/O ports when not used for the oscillator. Robin Abbott - robin.abbott@dial.pipex.com ************************************************************************** * * Forest Electronic Developments * http://dspace.dial.pipex.com/robin.abbott/FED * ************************************************************************** ----- Original Message ----- From: John De Villiers To: Sent: 03 October 1999 01:35 Subject: Driving 7segment displays > This might sound like a stupid question, but at what speed can i drive > 7segment displays?? In my current analogue design i use a 4Hz clock to pulse > the displays, but using a pic this is a little difficult. > > Will the 7segment display anything at all if i switch them at say once every > 100 instuctions ( on a 10 Mhz clock )? I suppose it all depends on the duty > cycle. > > Also, do i have to connect anything to the two clock lines in a 16c84 if im > using the internal clock ? > > Thanx > > John