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'[AVR]: Simple serial port project?'
2001\03\29@110844 by Greg Miller

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    I am having a very diffictult time getting an at89c2051 to send characters to a PC via the serial port.  I'm using a MAX235 (no ext components), as the RS232 driver.
    The problem is, the PC doesn't recognize anything the 89c2051 sends out (not even garbage).  I've used a logic probe to verify data is actually being sent and appears on the RS232 side of the MAX235.
    I've tested the PC port by connecting TX to RX going through the MAX235, and it checks out OK.  The distance from the 89c2051 to the PC is only about a foot, so I don't think the line length is the problem.
    I'm pretty much stumped at this point and would appreciate any pointers, advice, etc.

    Below is the program I'm using (P1_7 is used to blink an LED so that I know it's running).

#include <at89x2051.h>

//#define BAUD 19200
//#define RELOAD 253    //19200
#define RELOAD 192    //300
//#define RELOAD 250 //9600

void main(){
  int x,j;

  TCON=0;
  TH1=RELOAD;
  TMOD=32;   //Timer 1=8 bit auto reload
  PCON=128; //Double baud rate
  //PCON=0; //don't Double baud rate
  SCON=64; //Enable serial
  TR1=1;
  P1_7=0;

  while(1){
     for(j=0;j<5;j++){
        TI=0;
        SBUF='A';
        while(TI==1){}
        for(x=0;x<10000;x++){}
     }
     TH1--;
     if(P1_7==0){
        P1_7=1;
     } else {
        P1_7=0;
     }
  }
}

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'[AVR]: Simple serial port project?'
2001\04\02@051346 by JP.BROWN
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Hi Greg!, the problem you are having could be due to the PC handshake
lines needing pulling up. Try this:

link pins 7 and 8, also link pins 4 and 6  (9 pin D type only)
or
 "       4 and 5,       "        6 and 20 (25 pin D type only)

Some PCs do not need this connection (they float to the right level)
other PCs will not play ball until these signals are taken care of.

----- John

On Thu, 29 Mar 2001, Greg Miller wrote:

{Quote hidden}

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