PICs on a bus . . . ?

[RussMartin]

Given: One PIC is "the boss", one port is defined as output. Some x others, "slaves", each having one port defined as input. They share an 8-bit parallel bus.

Any issues? And what is the fanout limitation?

[Melanie]

In theory, dozens... since the master PIC can sink/source 25mA and the slaves have relatively high impedance (2K-10K) inputs. However in practice this will depend on the Data Transfer Speed and the total loaded circuit capacitance. You 'may' need some Pull-Up's on the Bus. If you're breadboarding, you'll discover if it's needed, if you're laying down a PCB board as a starter, there's no harm in adding the holes for a SIL Resistor pack in case it's needed. I can confirm FOUR PICS on a (small two-wire) Bus without problems. Watch you don't use a Port on the Master which has an Open-Drain pin - otherwise you WILL need that external Resistor.

[BobK]

Hi Russ,

I recently built 2 systems that have 20 PICs reporting to 1 PIC on a 2 wire buss. One is Busy and the other is data. They work great!

Let me know if you need more info on this type of system.

BobK

[RussMartin]

Bob, I've sent you a PM on this so we won't clutter up the forum. I'll look forward to hearing from you.

Melanie, thanks for the reminder on pullup(s). I'm using the 16F87xA devices (so far), and the only open drain I see in the data sheet is RA4. Being a fussy creature of habit, I'll probably want to put 4.7K pullups on anything that resembles a parallel bus . . .

[rhino]

Sorry, but I had to chime in.... Does this sound like a bad Samuel L. Jackson movie to anyone else? Pics on a Bus..... Snakes on a Plane.

[Jerson]

Sorry, but I had to chime in.... Does this sound like a bad Samuel L. Jackson movie to anyone else? Pics on a Bus..... Snakes on a Plane.

Just taking it a lil' further, how about a Rhino in soup?

Hey I'm only jokin. So, don't get serious.

Jerson

[Archangel]

Bob, I've sent you a PM on this so we won't clutter up the forum. I'll look forward to hearing from you.

All the jokes aside, . . .
Lots of Noobies out here looking to learn from posts such as this - It's not clutter to us, Thank You.

[RussMartin]

My apologies--I wasn't intending to be rude! I sent a private message to Bob merely to request more details. I'm sure he would be happy to share with all . . .