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play songs on a peizo buzzer?
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SherpaDoug



Joined: 07 Sep 2003
Posts: 1640
Location: Cape Cod Mass USA

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PostPosted: Thu Dec 22, 2005 7:58 am     Reply with quote
Try:

X0R(portc, 0b000 0011);

Now it won't change any of the other bits. If portc is mapped to the actual port the XOR itself will change the port pins without affecting the tristate register.
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Mark



Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA

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PostPosted: Thu Dec 22, 2005 10:57 am     Reply with quote
Christophe wrote:
So,

that would be

output_high(C0);
output_low(C1);
X0R(portc, 1111 1111);

output(portC);

the problem is that all port C pins are changing and becoming outputs. I don't want that because they are used for other purposes.


This function is causing the problem
output(portC);

you will need to specify fast_io to prevent this and handle the tris register yourself.
mcafzap



Joined: 07 Sep 2003
Posts: 46
Location: Manchester, UK

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PostPosted: Fri Dec 23, 2005 7:11 am     Reply with quote
To avoid RMW problems on the I/O ports, here is my buzzer routine:
Code:
void shortbeep(void)
{
int8 t;
t = Port_A & 0xCF;
for(j=0; j<=250;j++)
   {
   Port_A = t | 0x20;
   Delay_Us(120);
   Port_A = t | 0x10;
   Delay_Us(110);
   }
Port_A = t;
}


Steve
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