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hentropy
Joined: 27 Oct 2004
Posts: 6
Location: Kuala Lumpur, Malaysia
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| How do you detect a parity error with a software USART? |
 Posted: Sat Oct 30, 2004 12:52 am |
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Hi guys,
I would really appreciate your assistance for this beginner's problem:
I'm using the software USART of a PIC16F874 to receive information for display on an LCD panel. I noticed that there are occasional errors in my transmission, so I decided to enable Even parity.
| Code: | #include <16f874.h>
#fuses XT,NOWDT,NOPROTECT,PUT,NOLVP
#use delay( clock=4000000 )
#use rs232( baud=1200, parity=E, bits=8, xmit=PIN_A4, rcv=PIN_A5, errors ) |
Unfortunately, RS232_ERRORS doesn't work with the software USART, giving an "Undefined identifier" compiler error (although the documentation says it's suppose to have some use). Therefore, I don't think I can test for any error conditions.
How would you guys do it? |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Sat Oct 30, 2004 8:15 am |
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| Quote: | | Unfortunately, RS232_ERRORS doesn't work with the software USART, giving an "Undefined identifier" compiler error |
From the documentation you can conclude the RS232_ERRORS variable in a No UART configuration only has a purpose when using 9 data bits and/or the FLOAT_HIGH option. You are using neither of these settings and therefor the variable is optimized away causing your error.
But then, you start wondering how the compiler can ever return a parity error... Being curious I looked into the code generated for the RS-232 software receive and it turns out the parity is not checked at all!!! The parity bit is just skipped and no checks are performed. I know the CCS documentation isn't perfect, but this omission surprises me a lot.
B.T.W. I checked in PCH v3.187 |
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hentropy
Joined: 27 Oct 2004
Posts: 6
Location: Kuala Lumpur, Malaysia
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| Posted: Sun Oct 31, 2004 10:06 pm |
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Thanks for your reply ckielstra. At least now i know there's _NO_ way to do that.
(I'm using PCM v 3.117.) |
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asmallri
Joined: 12 Aug 2004
Posts: 1660
Location: Perth, Australia
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| Posted: Mon Nov 01, 2004 4:26 pm |
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| Quote: | | ...At least now i know there's _NO_ way to do that. |
Not quite. You can code your own software uart - then you can do whatever you want |
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