Matrix user forums

Hi guys,

Can anyone tell me the average fan out of a PIC output pin?

I need to control up to 20 PIC based circuit boards from one PIC based "master" board. The furthest run would be be around 10 metres.

Most of the master control would be done serially (output RC7) plus a couple of general outputs.

I have used CMOS 4050B buffer chips in the past to succesfully transmit general outputs over around half the distance to fewer inputs

The serial transmission is my biggest concern, does anyone have any suggestions?

The "fan out" distance depends on transmission speed and environmental factors so an exact distance really can't be given. I have had success using a ST485 low power RS-485/RS422 Transceiver when high speed and long distances are involved. You can just try using the buffer IC (or the micro's comparators) to retransmit the serial signal at each PIC and see how well it operates. If you do that, I would start with low speed 9600 baud or less and use a crystal or resonator on each PIC since temperature differences might be a factor.