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'Pic Network ?'
1998\11\22@180451 by Spk41q

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Hello,

Need to connect several PIC (slaves)  with one master.

Any pointers ?

Thanks
Dan

1998\11\23@031202 by Jan Derogee

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Hello Dan,i'm currently working on a robot-project where every
electrical/mechanical part has it's
own PIC controlling the proces. All these PIC's are controlled by a
master PIC that
decodes the commands as recieved from mine computer (or terminal).
Everything is RS-232 (9600 bps)
based so it's easy to check the activity on the "network" I prefer to
call SPINE. The idea behind
this PIC-rs232-network is simple, the robot consists of easy removeable
parts that don't depend
on eachother, therefore the robot can loose several functions and still
be operational. If you are
interested i'll send you the code. Unfortunatly this code is not (yet)
under interrupt but i'm working
on that. The I/O is more important then the communication. It is still
in the development proces.

By the way, allmost no extra hardware needed (the hardware is mainly on
the PIC itself).

best regards, Jan Derogee (the Netherlands)

> Hello,
>
> Need to connect several PIC (slaves)  with one master.
>
> Any pointers ?
>
> Thanks
> Dan

1998\11\23@053956 by David W. Duley

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In a message dated 11/22/98 3:04:59 PM Pacific Standard Time, spam_OUTSpk41qTakeThisOuTspamAOL.COM
writes:

<< Hello,

Need to connect several PIC (slaves)  with one master.

Any pointers ?

Thanks
Dan

 >>
Hi Dan!
The best way to do this is with RS485.  It allows multi-drop type networking.
In the machine that I build at work we have 14 pics all networked together
using RS485.  The protocol can be quite simple providing there is one master
and as many slaves as you need.  The real software tricks come in if there
needs to be more than one master.
We use the MAX485 chips in half duplex mode (2 wire)

Hope this helps
Dave Duley
http://www.dreitek.com

1998\11\23@054826 by Jeff Jolie

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Has anyone implemented a CAN network using PIC's?
Jeff Jolie
-----Original Message-----
From: David W. Duley <.....DREITEKKILLspamspam@spam@AOL.COM>
To: PICLISTspamKILLspamMITVMA.MIT.EDU <.....PICLISTKILLspamspam.....MITVMA.MIT.EDU>
Date: Monday, November 23, 1998 5:40 AM
Subject: Re: Pic Network ?


>In a message dated 11/22/98 3:04:59 PM Pacific Standard Time,
EraseMESpk41qspam_OUTspamTakeThisOuTAOL.COM
{Quote hidden}

networking.
>In the machine that I build at work we have 14 pics all networked together
>using RS485.  The protocol can be quite simple providing there is one
master
>and as many slaves as you need.  The real software tricks come in if there
>needs to be more than one master.
>We use the MAX485 chips in half duplex mode (2 wire)
>
>Hope this helps
>Dave Duley
>http://www.dreitek.com
>

1998\11\23@071802 by Peter Williamson

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So, what techniques are people using to make sure that the salve pics
always detect the start bit of a host request message even tho they
might be in the middle of doing something ??

Jeff Jolie wrote:
>
> Has anyone implemented a CAN network using PIC's?
> Jeff Jolie
> {Original Message removed}

1998\11\23@075225 by brad

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Peter Williamson wrote:
>
> So, what techniques are people using to make sure that the salve pics
> always detect the start bit of a host request message even tho they
> might be in the middle of doing something ??
>
Microchip App Note 555
Uses rtcc externaly clocked to detect start bit and generate interrupt.
I'm using it on an 84 and 71, at 9600 baud on RS485 with an 8mhz
crystal.
I have so much free processor time it's not funny.
I'm running a time sliced core which drives an external analog mux,
reads dipswitches
and writes leds and does it's a/d sampling. The pic is doing this on
it's ear.
The comms are a fairly simple master/slave protocol with variable length
messages and
simple checksums. I'm polling them with a PC under linux, and the pic is
so quick, I've had
to build a response delay into it to allow the linux box to turn off
it's rs485 transmitter.
In Linux I can do it in less than 10 msec. Under windows it was taking
over 100msec. The pic does
it in about 10 uSec :p)
Damn I wish I could run a pc that fast :p)

Anyway, my point in the above rambling, is that the MChip app note 555
is a pretty good
base to start from for half duplex, interrupt driven ascync IO.
It's really only interrupt driven recieve, as the tx byte routine blocks
anyway.

my .02c worth
--
-----------------------------------
Brad Campbell
Technical Manager

Seme Electrical Engineering Co
59 Collingwood St Osborne Park 6017
Western Australia
Ph    :-+61 8 9445 2577
Fax   :-+61 8 9244 1327
Email :- bradspamspam_OUTseme.com.au

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1998\11\23@142954 by WF AUTOMACAO

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Spk41q@AOL.COM wrote:
>
> Hello,
>
> Need to connect several PIC (slaves)  with one master.
>
> Any pointers ?
>
> Thanks
> Dan

Wich family?

Miguel

1998\11\23@143020 by David W. Duley

picon face
In a message dated 11/23/98 4:18:14 AM Pacific Standard Time,
@spam@peterwKILLspamspamWAYBEAT.COM.AU writes:

<< So, what techniques are people using to make sure that the salve pics
always detect the start bit of a host request message even tho they
might be in the middle of doing something ?? >>

A goo interupt driven serial routine will do this.  You can also use a
hardware UART to generate the interupt.  Maxim makes a cute little UART for
embedded applications. (MAX3100)

Dave Duley

1998\11\30@161328 by John Payson

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|So, what techniques are people using to make sure that the salve pics
|always detect the start bit of a host request message even tho they
|might be in the middle of doing something ??

One handy trick (for some applications) is to have the slaves always
listening for incoming data except when a command is sent which says,
in essense, "now go do stuff".  Once that command is sent, the master
must then refrain from sending data over the bus or else it might not
be heard.  The "now go do stuff" may be implicit in some or all comm-
ands, or it may be explicit (e.g. if your PICs are controlling stepper
motors, you could have commands to load each PIC's intended position,
and then a command to make them all go "there").

Another trick, if each command/packet is preceeded by a null or break
in addition to some other form of block header is to have the slave
units check  the state of the communications line in their main loop.
If it's high, the master isn't in the process of sending a null or
break.  The slaves then only need to check the line fast enough to
ensure that they don't miss the entire null or break; they may get a
fair number of false triggers (since the line will sometimes be low
because the master's sending other data) but as soon as the slave finds
out it false-triggered it can resume its main loop.

Both of these tricks can be very useful if the slave units have to perform
tasks like RC pot measurement which are time critical while they're being
done, but which do not need to be done at absolutely regular intervals.  In
some cases, of course, other methods will be more suitable.

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