uart multi slave (pic16f887)

khanh my · Joined: 01 Apr 2013 Posts: 13

please give me one sample code using uart or rs485
slave 1 sends one to master
slave 2 send 2 to the master
master two of them on screen display lcd

Mike Walne · Joined: 19 Feb 2004 Posts: 1785 Location: Boston Spa UK

I can't see your picture (or I got fed up of waiting for it to load).

khanh my · Joined: 01 Apr 2013 Posts: 13

Mike Walne · Joined: 19 Feb 2004 Posts: 1785 Location: Boston Spa UK

Should have asked earlier.

1) Are you using REAL hardware?
OR
2) Is it ALL ISIS simulation?

Mike

khanh my · Joined: 01 Apr 2013 Posts: 13

khanh my · Joined: 01 Apr 2013 Posts: 13

Mike Walne · Joined: 19 Feb 2004 Posts: 1785 Location: Boston Spa UK

I can now see your schematic more clearly.
You appear to be trying to connect as I showed in my ASCII version.
It is possible, but NOT the way to go.

It's been suggested several times already to use real interface devices and dedicate a pin to control the enable for each of your TTL to RS485 devices.

Nobody here is going to give you sample code.

You must get the hardware sorted before attempting code.

Mike

temtronic · Posted: Tue Apr 02, 2013 5:31 pm

Mike is 100% right, you MUST get the hardware corrected first !!

1) be sure to bias the RS-485 lines according to specs.

2) PICs as shown in your schematic will NOT run.

3) start with just 2 PICs,get working 100% THEN add the 3rd PIC.

hth
jay

ezflyr · Joined: 25 Oct 2010 Posts: 1019 Location: Tewksbury, MA

Hi guys,

I'm pretty sure this is a simulation effort only. I suspected as much, so I asked for a photo of the real hardware. The OP posted a broken link to his photo, and has since ignored a request to correct the link. I'm pretty sure he did this because there is no actual hardware, so this whole thread is probably a waste of time..... Hopefully, the OP will prove me wrong, but I doubt it!

John

temtronic · Posted: Tue Apr 02, 2013 8:04 pm

or he has real hardware , wired according to the 'simulation' schematic !
In which case it can never,ever work.

jay

khanh my · Joined: 01 Apr 2013 Posts: 13

ezflyr · Joined: 25 Oct 2010 Posts: 1019 Location: Tewksbury, MA

Hi,

I think it's pretty clear that there is no "real hardware", and that this is a pure Proteus simulation. That violates the forum rules because we don't want to be troubleshooting Proteus issues here, only CCS ones.

Another problem is that you seem to want someone to just hand you some working code, and we don't do that here either. Everything you've posted so far suggests that you are just cobbling together code you have found without any understanding at all....

The schematic you posted is also not correct. Did you even search the internet for the suggested way to connect the MAX487? For example, I'm not sure I've ever seen an implementation that does not tie pins 2 and 3 together.....

Good Luck!

John

Mike Walne · Joined: 19 Feb 2004 Posts: 1785 Location: Boston Spa UK

Im assuming you actually have power connected to your RS485 devices.
(It's not shown on your schematic.)

I'm not going to GIVE you sample code.

At the risk of being sent to the tag-team naughty corner I advise:-

a) Sort out your code one section at a time.
b) Get it 100% correct, then proceed.
c) Do as temtronic suggested a while ago.
Get your master to talk to one slave only then progress to more slaves.

A very simple version of your code could go something like this:-

Master asks Slave1 to transmit:-

1) Slaves all disable their TX control.
2) Master enables its TX control.
3) Master tells all slaves it wants slave1 to transmit by sending out say a character '1'.
4) Slave1 receives and recognises character.

In response Slave1 transmits:-

5) Master disables its TX control.
6) Slave1 enables its TX control.
7) Slave1 sends a known return character.
8) Master receives and recognises character.
9) Loop back to 1.

If you do all of the above in a tight loop you SHOULD be able to watch all the activity on any 'scope.
It will check your hardware is functional.

Mike

temtronic · Posted: Wed Apr 03, 2013 3:07 pm

re: individual control of re and te(rcv enable, tx enable).

It does allow for some nice multimaster-multislave control under software though these days the 'rs-485' chips can have an active rcvr.
I used it back in the early days (PCM 2.459ish) for a proprietory system, still in use today.

The key or trick with 3 or more PICs is to divide and conquour! Start small,get 2 working, then 3, 4,...128,though the most I've had in the field has been 62 nodes.

There is a LOT of threads on this subject,some great code,even CCS has examples so I suspect a 'hardware' issue is the basis of the problem.

hth
jay

khanh my · Joined: 01 Apr 2013 Posts: 13

thanks all
I also want to support CCS, but the hardware you asked so I gave up, my project is more complex, but I have know communication rs485 to ask, I asked simple matter to develop my project,
I am a student doing thesis for graduation