Multi drop serial bus

[Doorman352]

I asked a week ago about how to implement a multidrop design to use a serial
bus to communicate between multiple boards scattered across an area. I got a
lot of great ideas...the best seemed to be RS485.

I don't seem to be able to find anything on the development of such a
bus....or the means to utilize it in a scenario.

I found tons of data on what it does and can do, and a few schematics, which
lack enough detail to derive my configuration.

I am trying to build a master controller and a series of sub boards, that
are addressed and controlled. I want to have 2 way communications with the
boards and be able to reset all or 1 if necessary. I am trying to avoid
embedding PICs in my design as I can't simulate my schematics with PICs.

I can't find any simulation programs that can simulate an RS485 chip
either....

I am not a heavy designer, nor am I a heavy application developer. I just
want to build a crude prototype so I can see if my idea is feasible.....and
I'm not getting anywhere.

Anybody with a whole lot of patience and a few minutes want to bounce some
ideas back to me...... Please.


Doorman352

 

[CFoley1064]

Subject: Multi drop serial bus
From: "Doorman352" doorman352@earthlink.net
Date: 5/4/2004 9:44 PM Central Standard Time
Message-id: <dyYlc.7490$V97.3759@newsread1.news.pas.earthlink.net

I asked a week ago about how to implement a multidrop design to use a serial
bus to communicate between multiple boards scattered across an area. I got a
lot of great ideas...the best seemed to be RS485.

I don't seem to be able to find anything on the development of such a
bus....or the means to utilize it in a scenario.

I found tons of data on what it does and can do, and a few schematics, which
lack enough detail to derive my configuration.

I am trying to build a master controller and a series of sub boards, that
are addressed and controlled. I want to have 2 way communications with the
boards and be able to reset all or 1 if necessary. I am trying to avoid
embedding PICs in my design as I can't simulate my schematics with PICs.

I can't find any simulation programs that can simulate an RS485 chip
either....

I am not a heavy designer, nor am I a heavy application developer. I just
want to build a crude prototype so I can see if my idea is feasible.....and
I'm not getting anywhere.

Anybody with a whole lot of patience and a few minutes want to bounce some
ideas back to me...... Please.


Doorman352

I read you as saying you want to have a master controller communicate with
multiple "sub boards" without having a PIC or other processor on the "sub
board" side to read and interpret the communication, as well as doing error
checking and resetting the I/O on command.

Just about the only way you're going to be able to do that with LSI/MSI ICs and
discrete components is to make a PIC or other rudimentary processor out of
those components. If you just want to use the RS-485 balanced transmission
technique to set up remote shift registers and such, you're going to need a lot
more than one pair of wire.

The way to emulate a processor in a circuit is to use an emulator written for
that processor. The way to test and debug a program you've written in a
circuit is to use an ICE (In-Circuit Emulator). Both of these are available
for very reasonable prices for the PIC.

If this is a real project and not just a school exercise, I'd like to recommend
that you Google "RS-485" +"Remote I/O", and look at the results. There are a
number of manufacturers that make these remote I/O boards already built and
tested for less than $100 USD each. And yes, all of them have PICs or other
low end processors on board to handle the comm chores. Get an RS232-to-RS485
adapter for your PC serial port from the same source, and you've now got
nothing more than a programming problem.

http://www.lvr.com/serport.htm

Good luck
Chris

 

[Pieter Hoeben]

On Wed, 05 May 2004 02:44:25 GMT, "Doorman352"
<doorman352@earthlink.net> wrote:

I asked a week ago about how to implement a multidrop design to use a serial
bus to communicate between multiple boards scattered across an area. I got a
lot of great ideas...the best seemed to be RS485.
Hi, RS485 is only the hardware part of a bus. On that bus a prorocol

must run. You can do asynchronous communication (what one often
does with RS232 hardware) or synchronous communication like
several networks, Profibus, Bitbus etc.

I don't seem to be able to find anything on the development of such a
bus....or the means to utilize it in a scenario.
So RS485 is not a bus, it is only the hardware.

I found tons of data on what it does and can do, and a few schematics, which
lack enough detail to derive my configuration.
I am trying to build a master controller and a series of sub boards, that
are addressed and controlled. I want to have 2 way communications with the
boards and be able to reset all or 1 if necessary. I am trying to avoid
embedding PICs in my design as I can't simulate my schematics with PICs.
I will show an example here I often worked with:

the good old Bitbus (from 1984, way ahaed of its time, people never
really understood the possibility's): It uses RS485 as hardware layer.
The software talks with synchronous SDLC packets, a subset of HDLC,
looks like something on your Ethernet. It is a single master system
(no collision detection) but can have outstanding messages slaves can
reply to, and therefor still have 2-way communication. The chip I
often use is the 8044 (Intel used to make it, we distribute it a
replacement device for it): it already contains the iDCX51
multitasking operating system with a pre-programmed Bitbus
communication task. One of the things that task can do is a reset of
the microprocessor, as you asked. It can also read/write memeory, i/o,
download firmware, start and stop tasks etc. And that all over the
rs485 network at 380 KBit, or 1.5 MBit.

So you see: it probably is more work than you think! But there already
are solutions. Several.

I can't find any simulation programs that can simulate an RS485 chip
either....
I am not a heavy designer, nor am I a heavy application developer. I just
want to build a crude prototype so I can see if my idea is feasible.....and
I'm not getting anywhere.
So what do you want to build?

Anybody with a whole lot of patience and a few minutes want to bounce some
ideas back to me...... Please.
Doorman352

Pieter Hoeben
email: pieter@hoeben.com
http://www.hoeben.com