PIC16F630 and RS232

Fabri · Joined: 22 Aug 2005 Posts: 275

Hi Everybody,

This is a first time I use RS232 in software with CCS compiler.

I'm using RS232 in PIC16F630 without USART with internal RC oscillator 4 Mhz.

Fabri · Joined: 22 Aug 2005 Posts: 275

Hi,

Because I use an RTCC interrupt every 200uS, I disabled it and the comunication start to work correctly.

I stay in interrupt 26 uS, just to take a count of time.

Why does it?

Thanks,

asmallri · Joined: 12 Aug 2004 Posts: 1634 Location: Perth, Australia

Ttelmah · Guest

Also, the actual interrupt tie will be longer than 26uSec. I'd suspect this is the duration in the 'handler', rather than the total interrupt time. On a PIC, when an interrupt occurs, the global handler is called, which saves the registers, then calls the actual 'event handler'. When this finishes, the code returns to the global handler, which clears the interrupt flag, restores the registers, and finally returns to the main code.
Unfortunately, even if the event handler itself, only takes 26 instructions, the global handler will typically add perhaps another 50uSec to this. With an RTC at 200uSec, and an event handler that lasts 26uSec, the processor will be in the global handler and the event handler for this, about 76uSec out of every 200uSec. About 1/4 the processor time.....

Best Wishes