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helmi03
Joined: 12 Apr 2011
Posts: 7
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| RS485 communication between 1 master (PC) and 3 slave |
 Posted: Tue Apr 12, 2011 2:41 pm |
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hi, I'm new in embedded c and I have to establish a communication between 3 slave (pic16F877) and 1 master (PC) via RS485. The problem that I try so much solution from this forum and no one is working for me:
http://img34.imageshack.us/i/sheman.png/
I'm now working just for receive information from rs232 and transmit with RS485 just to 1 pic.
My project is to send information to 3 pic and with address and the one with rue address only get information and reply to master.
* sorry for my bad english |
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cerr
Joined: 10 Feb 2011
Posts: 241
Location: Vancouver, BC
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| Re: RS485 communication between 1 master (PC) and 3 slave |
| Posted: Tue Apr 12, 2011 3:08 pm |
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| helmi03 wrote: | hi, I'm new in embedded c and I have to establish a communication between 3 slave (pic16F877) and 1 master (PC) via RS485. The problem that I try so much solution from this forum and no one is working for me:
http://img34.imageshack.us/i/sheman.png/
I'm now working just for receive information from rs232 and transmit with RS485 just to 1 pic.
My project is to send information to 3 pic and with address and the one with rue address only get information and reply to master.
* sorry for my bad english |
Hi helmi03,
Well, I won't do work FOR you but I might be able to assist you or direct you into the right direction. You're wondering how to communicate with rs 232. Check #USE RS232 in the CCS manual. You also wanna look at functions like fputc(), fgetc(), printf() or kbhit(). You might also wanna look at the example ex_RS232_485.c in the examples directory |
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ezflyr
Joined: 25 Oct 2010
Posts: 1019
Location: Tewksbury, MA
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| Posted: Tue Apr 12, 2011 3:12 pm |
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Hi,
This is a pretty easy project actually. What you want is a Master-Slave half-duplex arrangement, ie. nobody "talks" on the bus except the Master, unless asked to do so.
You need to design a simple command protocol that the Master will use to communicate with the Slaves. You can make your life much easier by doing this intelligently. In the past I've used something like this:
#SLVX:CMD<Cr>, where 'X' is the address 1, 2, or 3. The important parts here are the Start Character '#', and the End Character 'Cr' - your receive routines will use them to know when a command string starts and ends.
Your picture was too small even when enlarged, but it appears that you are using the RS485 transceiver incorrectly. Pins 2 and 3 can be tied together, and then controlled by a digital output on the PIC. This allows you to control the direction of data on the bus. The #USE RS232 statement can be configured to include the direction control automatically.
Oh, is this exclusively a Proteus project, or will you also do this in real hardware?
John |
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helmi03
Joined: 12 Apr 2011
Posts: 7
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| Posted: Tue Apr 12, 2011 3:22 pm |
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thank you for answer me, i will try this for real .
@cerr i try so much code but no one is working correctly for me. example :
| Code: |
#include <C:\Program Files\PICC\Devices\16F877.h>
#fuses HS,NOWDT,NOPROTECT,NOLVP
#use delay(clock=10000000)
#use rs232(baud=9600,xmit=PIN_C6, rcv=PIN_C7, stream=PC)
#define RS485_RX_BUFFER_SIZE 64
#define RS485_USE_EXT_INT FALSE
#define RS485_ID 0x09
#define ADAPTER_RS485_ID 0x7f
#define RS485_RX_ENABLE PIN_B5
#define RS485_ENABLE_PIN PIN_B4
#define RS485_TX_PIN PIN_C6
#define RS485_RX_PIN PIN_C7
#include <C:\Program Files\PICC\Drivers\rs485.c>
#include <C:\Program Files\PICC\Drivers\stdlib.h>
int8 msg[32];
char RS485getc() {
rs485_get_message(msg, TRUE);
return msg[2];
}
char h;
void main()
{
output_low(RS485_RX_ENABLE);
set_tris_a(0x00);
output_low(RS485_ENABLE_PIN);
rs485_init();
while(true)
{
h=RS485getc();
output_a('h');
}
} |
and try so much other code i just won't to send a number and this number will be display in the 7seg.
i tried the ex RS485-232 but i think i didn't use it correctly.
can some one please explain to me what this function do
fputc() to write in output
fgetc() to read
, printf() ??
or kbhit() ??
Thank you |
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cerr
Joined: 10 Feb 2011
Posts: 241
Location: Vancouver, BC
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| Posted: Tue Apr 12, 2011 3:25 pm |
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| helmi03 wrote: |
can some one please explain to me what this function do
fputc() to write in output
fgetc() to read
, printf() ??
or kbhit() ??
Thank you |
I would suggest you look at the manual. That should help you! |
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bkamen
Joined: 07 Jan 2004
Posts: 1615
Location: Central Illinois, USA
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| Posted: Tue Apr 12, 2011 7:11 pm |
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you also want to look closer at #USE RS232 in the manual and it's option ENABLE which will do an RS485 enable for you.
-Ben
_________________
Dazed and confused? I don't think so. Just "plain lost" will do. :D |
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