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whmeade10
Joined: 27 Jan 2004
Posts: 12
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| Wierd Echo on RS-232 Transmission |
 Posted: Thu Sep 13, 2007 7:28 am |
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I am exchanging ASCII information with a GE FANUC PLC via RS-232. I receive a 'P1 and return character' from the PLC and I attempt to send information back. What is happening, and I can't figure it out, is I am sending the P1 I received then the data is attached. Is there a buffer I have to clear?
Example: Receive - P1 then return character
Transmit - P1029640006100781 and a return
I can't figure out how the P1 is being sent. My code is below. I am using version PCWH Compiler v4.053.
| Code: |
#include <18F452.h>
#use delay(clock=20000000)
#fuses HS,PROTECT,NOLVP,PUT,BROWNOUT, NOWDT // set fuses
#use rs232(baud=9600,xmit=PIN_C6,rcv=PIN_C7,ERRORS) // setup serial communications
#include <string.h>
#include <input.c>
// ********** DEFINE VARIABLES ***********************************************************************
byte i;
int16 adc_value, pulse_count, ms_final, scale_no;
// ********** START OF MAIN PROGRAM ******************************************************************
void main()
{
char input_str[3]; // set max serial input string to 2
adc_value = 2964;
pulse_count = 61;
ms_final = 78;
scale_no = 1;
while(TRUE) // start of continious loop
{
Get_string(input_str,3); // gets the string
If ((input_str[0] == 'P') && (input_str[1] == '1')) // check incomming serial data for POLL
{
printf("%05lu%05lu%04lu%01lu\r", adc_value, pulse_count, ms_final, scale_no,);
} // end of IF statement
} // end of program loop
} // main end |
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Ttelmah
Guest
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| Posted: Thu Sep 13, 2007 8:39 am |
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Ignoring anything else, your input string needs to be larger. A 3 character string, requires _4_ characters of storage (to include the terminating '\0'). the 'Get_string' function, called with '3' as the length limit, needs _4_ characters of storage.
The reason you are getting the P1 echoed, is that this is what 'Get_string' does. It is designed to get a string being typed in at the other end, and echo the characters. Look at it's code. Every character that is getc received, it immediately sent out again. Simple take tget Gt_string code out of input.c, and make your own version, with the 'putc' entries removed.
Best Wishes |
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whmeade10
Joined: 27 Jan 2004
Posts: 12
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| Posted: Thu Sep 13, 2007 9:18 am |
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| Thanks Ttelmah for the quick reply. I changed the get_string function and increased the string length from 3 to 4 and everything is working perfectly. Thanks agan for taking the time to answer my question. |
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