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Tomson
Joined: 09 May 2007
Posts: 6
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| getc reads only trash |
 Posted: Wed Apr 30, 2008 2:42 am |
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Hi,
I'am trying to get a char over the rs232 interrupt INT_RDA of my pic. But what ever I sent to the controller by HyperTerminal, it gets only a 0xFF.
I'am using a PIC18F2480 and a CCS PCWH Compiler in the version 4.062.
I've done a small project, to show the problem more detailled.
Can anybody help my.
Thanks a lot.
Regards Tomson
| Code: | #include "18F2480.h"
#fuses HS, PROTECT
#fuses BROWNOUT
#fuses WDT128, BORV42
#fuses PUT, NOCPD, STVREN, NODEBUG
#fuses NOLVP, NOWRT, NOWRTD, NOIESO, FCMEN
#fuses NOPBADEN, BBSIZ1K, NOWRTC, NOWRTB, NOEBTR
#fuses NOEBTRB, CPB, NOLPT1OSC, MCLR
#fuses NOXINST
#use delay(clock=12000000, RESTART_WDT)
#use fast_io(A)
#use fast_io(B)
#use fast_io(C)
#use RS232(baud=2400, xmit=PIN_C6, rcv=PIN_C7, BITS=8, PARITY=E, RESTART_WDT)
//***********************************************************************************
//** global variables
//***********************************************************************************
char dummy;
//***********************************************************************************
//** interrupt service routine
//***********************************************************************************
#int_rda
void rx_isr()
{
dummy = getc(); // the result of the getc command is always 0xFF!
}
//***********************************************************************************
//** main program
//***********************************************************************************
void main(void)
{
#zero_ram
//***********************************************************************************
//** Set Port C directions
//***********************************************************************************
SET_TRIS_C(0b10010010);
//***********************************************************************************
//** Start WatchDog
//***********************************************************************************
SETUP_WDT(WDT_ON);
//***********************************************************************************
//** Enable interrupts
//***********************************************************************************
enable_interrupts(INT_RDA);
enable_interrupts(GLOBAL);
//***********************************************************************************
//** Send a test message
//***********************************************************************************
printf("\n\n\r Test program"); // This works fine!
//***********************************************************************************
//** Start main loop
//***********************************************************************************
do
{
if (dummy != 0)
{
putc(dummy);
dummy = 0;
}
//***********************************************************************************
//** restart WatchDog
//***********************************************************************************
RESTART_WDT();
} while(True);
} |
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Matro
Guest
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| Posted: Wed Apr 30, 2008 2:50 am |
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Check carefully that the PC has exactly the same settings as the PIC.
how is done the level shifting between PC and PIC?
Matro |
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Tomson
Joined: 09 May 2007
Posts: 6
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| Posted: Wed Apr 30, 2008 2:56 am |
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Hi Matro,
thank you for your fast reply. The hyperterminal and the pic has the same RS232 settings. 2400, 8E1. The communication from PIC to PC works fine. I sent a short message at the start of the program that is received well by HyperTerminal.
Level shifting is done with a MAX232 derivate that works fine in other projects.
Tomson |
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Matro
Guest
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| Posted: Wed Apr 30, 2008 3:13 am |
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Could you try the posted code but without :
- the 3 "#use fast_io" lines
- the "set_tris_c" line
Did you already have a look at the incoming signals with a scope?
Matro |
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Tomson
Joined: 09 May 2007
Posts: 6
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| Posted: Wed Apr 30, 2008 3:33 am |
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There is no change in the behavior after I've outposted the suggested lines.
I've looked at the incoming signal with the scope and recognized that this was very strange. I've to look more detailled for it.
Thank you very much.
Regards Tomson |
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Matro
Guest
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| Posted: Wed Apr 30, 2008 3:44 am |
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I definitely suspect a hardware issue.
Matro |
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Tomson
Joined: 09 May 2007
Posts: 6
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| Posted: Wed Apr 30, 2008 3:47 am |
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Hi Matro,
at the moment I think the same. I will do some tests on the board.
Thank you very much for your help.
Regards, Tomson |
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Douglas Kennedy
Joined: 07 Sep 2003
Posts: 755
Location: Florida
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| Posted: Wed Apr 30, 2008 11:57 am |
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| char dummy is not initialized. Look at setting a global flag in the RDA isr to indicate a char has been read. Initialize the global flag and clear it main after you have processed the value in dummy. It is very likely that the issue lies with your receive hardware but tightening up the software might help also. |
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baltazar_aquino
Joined: 16 Mar 2008
Posts: 27
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| Posted: Fri May 02, 2008 10:03 pm |
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This is really more likely a hardware problem. I've experienced the same issue and later on found out the following:
1: Wrong connection of TX-RX (reversed) pins between the D9 connector & the MAX 232 chip.
2. I used a transistor level converter instead of a dedicated chip . Sometimes this type of converter cannot drive the D9 port properly to acceptable RS-232 mark and space levels. (This is especially true if you are using a USB-RS232 converter- as in a laptop).
Kindly refer to this topic.
http://www.ccsinfo.com/forum/viewtopic.php?t=34110&highlight= |
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