MAX232 and AT commands

[thunderfsi]

Hi everyone, I'm having a problem on my circuit. I send AT commands from PIC. After they pass MAX232 "AT" turns into "_" and enter command turns into "y". I'm new to these stuff. Can anyone please help ?

Circuit: View attachment v1.3.rar

sbit LCD_RS at RC0_bit;                 // LCD_RS assigned to PORT RC0;
sbit LCD_EN at RC1_bit;                 // LCD_EN assigned to PORT RC1;
sbit LCD_D4 at RC2_bit;                 // LCD_D4 assigned to PORT RC2;
sbit LCD_D5 at RC3_bit;                 // LCD_D5 assigned to PORT RC3;
sbit LCD_D6 at RC4_bit;                 // LCD_D6 assigned to PORT RC4;
sbit LCD_D7 at RC5_bit;                 // LCD_D7 assigned to PORT RC5;

sbit LCD_RS_Direction at TRISC0_bit;    // LCD_RS assigned to TRIS C0;
sbit LCD_EN_Direction at TRISC1_bit;    // LCD_EN assigned to TRIS C1;
sbit LCD_D4_Direction at TRISC2_bit;    // LCD_D4 assigned to TRIS C2;
sbit LCD_D5_Direction at TRISC3_bit;    // LCD_D5 assigned to TRIS C3;
sbit LCD_D6_Direction at TRISC4_bit;    // LCD_D6 assigned to TRIS C4;
sbit LCD_D7_Direction at TRISC5_bit;    // LCD_D7 assigned to TRIS C5;

#define OSC 20

void main(){

     ADCON1 = 0x06; //Analog to Digital Conversion
     TRISA=0xFF;   //Set PORTA as Input
     TRISB=0x00;   //Set PORTB as Output
     TRISC=0x80; //set direction of PORTC6 as output -- TX -- transmitter //set direction of PORTC7 as input -- RX -- reciever
     TRISD =0x00;
     TRISE =0x00;

     
     RB0_bit=0;
     
     UART1_init(9600);  // Initialize UART at 9600bpm
     delay_ms(1000);
     Lcd_Init();
     Lcd_cmd(_LCD_CLEAR);
     Lcd_cmd(_LCD_CURSOR_OFF);

     UART1_Write_Text("AT");
     delay_ms(1000);
     UART1_Write(0x0D); // ENTER
     delay_ms(2000);

     Lcd_Out(1,1, "Message Sent");
     delay_ms(3000);

     Lcd_cmd(_LCD_CLEAR);
     Lcd_cmd(_LCD_CURSOR_OFF);
}

 

[siongboon]

It is very much a timing or clk problem.
Check with your scope the data rate if it is 9600 as you have set.
Then check all your clk, UART settings again.

 

[Gorgon]

What do you read the data with, a PC?
The max232 only inverts the logic(logic1=-v and logic0=+v), and does not add anything to the data itself.
If you read one character for the two sent, there is a mismatch in baudrate between the sender and the receiver.

 

[Surender Reddy]

The problem should be with baudrate mismatch of the PIC & the PC.
For PIC use 9600 and check in PC for 9600, baudrate should match.....
check it once.......