ATmega16A uses the process PC port to solve

I was recently busy with a project using ATmega16A, and found a very strange problem: the 4 PC ports of M16 (PC2, PC3, PC4, PC5, corresponding to the 4 pins of JTAG) cannot be used normally. There are no problems with the software and fuse settings. When the JTAG pin is disabled, the PC5 pin inexplicably outputs the wrong level (when PC5 outputs a high level, the pin voltage is only 2.54V). At first, I thought it was caused by a wrong fuse bit. I redesigned it again, and there were no problems, but the problem still occurred. Finally, the method I found was to turn off JTAG in the software, and write MCUCSR|=0x80; twice to succeed. It can be determined that JTAG is not turned off. Now I know that the fuse is confirmed to be turned off, but there is no explanation for this situation. Now the guess is: the IC may be refurbished, the software is turned off, and MCUCSR |= 0x80; is written twice;

Hardware Description: ATmega16A 8MHZ crystal oscillator

Compilation environment: ICCV7 for AVR

The fuse settings are as follows:

test program:

#include  

#include  

#include  

#define uint unsigned int  

#define uchar unsigned char  

void delay(void)  

{  

  unsigned int i,j;  

  for(i=0;i<100;i++)  

    for(j=0;j<1000;j++)  

      {;}  

}  

int main(void)  

{  

  PORTC=0x00;  

  DDRC=0xFF;   

  MCUCSR |= 0x80; // Software disables JTAG  

  MCUCSR |= 0x80;  

  delay();  

 while(1)  

   {  

     PORTC=~PORTC;  

     delay();  

   }  

   return 0;  

}