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Fabri
Joined: 22 Aug 2005 Posts: 275
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PIC16F630 and RS232 |
Posted: Tue Dec 13, 2005 2:30 am |
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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.
Quote: |
#use delay(clock=4000000, RESTART_WDT)
#use rs232(baud=9600, xmit=PIN_C4,rcv=PIN_C3)
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the PIC send out a character but it isn't 9600 baud and the PC doesn't see the comunication.
One character at 9600 baud take 1,87 ms time, my pic send the same character in 1,37 ms.
I'm using PCWH V3.235.
Have you something to suggest me ?
Thanks for support, |
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Fabri
Joined: 22 Aug 2005 Posts: 275
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Posted: Tue Dec 13, 2005 2:55 am |
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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, |
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asmallri
Joined: 12 Aug 2004 Posts: 1634 Location: Perth, Australia
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Posted: Tue Dec 13, 2005 3:04 am |
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Fabri wrote: | 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, |
You have answered your own question. I am not sure about the specific numbers you have mentioned but every 200us you spend 26us in the interrupt handler. The software UART counts bit time in software. It is not able to determine that the the interrupt handler has repeasted interrupted the process.
At 9600 baud a standard 8 bit no parity character transmission takes 1.04ms including the start and stop bit. Five or 6 interrupts will occur during this period adding an additional 120us to 156us plus the call return overhead if you have not already included this in your number. _________________ Regards, Andrew
http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!! |
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Ttelmah Guest
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Posted: Tue Dec 13, 2005 4:58 am |
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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 |
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