connect 20 pics

kloppy · Joined: 28 Jul 2004 Posts: 32

what is a good way to communicate with 20 pics? I need only one master and it hasn't to be fast. the distance between the first and the last pic ist between 0.5 an 1 meter

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

I2C or SPI are easy to impliment. 485 is overkill for the short distance. You get best speed with a parallel bus but it will use a lot of pins.
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PCM programmer · Joined: 06 Sep 2003 Posts: 21708

See this article in the CCS FAQ:
http://www.ccsinfo.com/faq/?23

If you search google for these keywords: PIC network "multi-drop"
there are several good web pages. Here is one:
http://jap.hu/electronic/pbus.html

Darren Rook · Joined: 06 Sep 2003 Posts: 287 Location: Milwaukee, WI

Ok, I gotta know... What are you doing that you need 20 PICs within 1 meter of each other?

Mark · Joined: 07 Sep 2003 Posts: 2838 Location: Atlanta, GA

We do it with lighting controllers

http://www.lithonia.com/Controls/synergy/Products/enclosures.htm

jds-pic · Joined: 17 Sep 2003 Posts: 205

Darren Rook · Joined: 06 Sep 2003 Posts: 287 Location: Milwaukee, WI

Mark,

how many PICs in the big one?

Haplo · Joined: 06 Sep 2003 Posts: 659 Location: Sydney, Australia

We used RS485 to connect 16 PICs, with each PIC being about one meter apart from the next one. It worked very well.

kloppy · Joined: 28 Jul 2004 Posts: 32

i have 20 steppermotor controllers in a scanner with a pic on each controller.
i thought about i2c but i worry if the distance is already too long.

rnielsen · Joined: 23 Sep 2003 Posts: 852 Location: Utah

I have one project with an 18F452 talking to 10 16F87's. The 87's do all of the time intensive stuff (monitoring sensors) while the 452 simply requests data from each slave every second and then does the process controlling. All using I2C.

Ronald

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

Mark · Joined: 07 Sep 2003 Posts: 2838 Location: Atlanta, GA

We use 6ma active pullups

kloppy · Joined: 28 Jul 2004 Posts: 32

what do you think about twisted pair connections?

Yashu · Joined: 08 Oct 2003 Posts: 26

crying out for single wire CAN

J_Purbrick · Joined: 16 Sep 2003 Posts: 9

A method that I'm using for about 20 PICs communicating with a computer is "modified RS422" where the master (the computer) can talk any time it wants to, using packets containing an address. Every character is received by every PIC, and each PIC checks for the address, and responds only to packets addressed to it. Simple enough.

For data back to the master, there's a "hardware token" that is generated by the processor closest to the computer. It's a positive-going pulse that's sent out 10 times a second, and while sending it, the PIC has the authority (in fact, a requirement) to enable its driver onto a shared line and send a packet to the master. When the PIC completes its packet, it sends the token line feeding the next PIC low, which starts that processor's communication sequence. The packet sent by a PIC contains its address, so the master knows who said what, regardless of the order of PICs on the network. Clearly, there are limitations on what this network can achieve, but it's suitable for the purpose.

The network runs at 115.2KB and hence is compatible with an ordinary serial port, with just the need for RS232 to RS422 level conversion.