PIC16F722A . PORTB Bits not latching

[1230]

hi all...
writing a simple code to make understand the problem.
PORTB bit 4 should remain high all the time. but its going low after making change to portb. bit5.
cannot trace the problem, pls help.

int main()
{
TRISB=0X00;

PORTB |=(1<<4);
Delay_ms(2000);

while(1)
{
PORTB |=(1<<5);
}
}

 

[betwixt]

Probably a RMW problem which is well documented. The PIC16 series doesn't simply set individual bits when you write to a port, it reads the whole port, sets the bit then writes it all back again. If bit 4 is externally floating low or pulled low, the write (OR operation) to bit 5 reads bit 4 as zero so it writes it back as zero.

The PIC18 series uses LAT registers to overcome the problem but the simple solution to your issue is to keep a variable for the bit operations and write it to PORTB whenever you change its contents.

Brian.

 

[1230]

Probably a RMW problem which is well documented. The PIC16 series doesn't simply set individual bits when you write to a port, it reads the whole port, sets the bit then writes it all back again. If bit 4 is externally floating low or pulled low, the write (OR operation) to bit 5 reads bit 4 as zero so it writes it back as zero.

The PIC18 series uses LAT registers to overcome the problem but the simple solution to your issue is to keep a variable for the bit operations and write it to PORTB whenever you change its contents.

Brian.

Thanks sir...
but i found the problem.
pic16 series write an individual pins of a port. in my code, i have to disable the ANSELB registor. after disabling my problem solved