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Thoman
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| HW & SW rs232 baudrate error? |
 Posted: Sat Nov 22, 2008 7:09 pm |
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Hi,
I'm trying to use 2 rs232 link on a 18f452 (one hard and one soft), yet I can't make it work  The SW works fine, but the HW receive just trash.
I dont have any idea left, what am I doing wrong?
| Code: |
#include <18F4520.h>
#device adc=8
#FUSES NOWDT //No Watch Dog Timer
#FUSES WDT128 //Watch Dog Timer uses 1:128 Postscale
#FUSES H4 //High speed Osc (> 4mhz) + PLL (x4)
#FUSES NOPROTECT //Code not protected from reading
#FUSES BROWNOUT //Reset when brownout detected
#FUSES BORV25 //Brownout reset at 2.5V
#FUSES PUT //Power Up Timer
#FUSES NOCPD //No EE protection
#FUSES STVREN //Stack full/underflow will cause reset
#FUSES NODEBUG //No Debug mode for ICD
#FUSES NOLVP //No low voltage prgming, B3(PIC16) or B5(PIC18) used for I/O
#FUSES NOWRT //Program memory not write protected
#FUSES NOWRTD //Data EEPROM not write protected
#FUSES NOIESO //Internal External Switch Over mode disabled
#FUSES FCMEN //Fail-safe clock monitor enabled
#FUSES PBADEN //PORTB pins are configured as analog input channels on RESET
#FUSES NOWRTC //configuration not registers write protected
#FUSES NOWRTB //Boot block not write protected
#FUSES NOEBTR //Memory not protected from table reads
#FUSES NOEBTRB //Boot block not protected from table reads
#FUSES NOCPB //No Boot Block code protection
#FUSES LPT1OSC //Timer1 configured for low-power operation
#FUSES MCLR //Master Clear pin enabled
#FUSES NOXINST //Extended set extension and Indexed Addressing mode disabled (Legacy mode)
#use delay(clock=38000000,RESTART_WDT)
#use rs232(baud=4800,parity=N,uart1,bits=8,stream=GPS,errors)
#use rs232(baud=4800,parity=N,xmit=PIN_D3,rcv=PIN_D2,bits=8,stream=PC,restart_wdt)
char Ch2;
int1 new;
#int_RDA
void RDA_isr(void)
{
Ch2=fgetc(GPS);
new=true;
}
void main()
{
setup_adc_ports(NO_ANALOGS|VSS_VDD);
setup_adc(ADC_OFF|ADC_TAD_MUL_0);
setup_psp(PSP_DISABLED);
setup_spi(SPI_SS_DISABLED);
setup_wdt(WDT_OFF);
setup_timer_0(RTCC_INTERNAL);
setup_timer_1(T1_DISABLED);
setup_timer_2(T2_DISABLED,0,1);
setup_timer_3(T3_DISABLED|T3_DIV_BY_1);
setup_comparator(NC_NC_NC_NC);
setup_vref(FALSE);
enable_interrupts(INT_RDA);
enable_interrupts(GLOBAL);
setup_oscillator(OSC_PLL_ON);
while(1)
{
if(new==true)
{
fprintf(PC," => %c \n\r",Ch2);
new=false;
}
}
}
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here is what the pic receive (sent back with the SW)
a => ü
b => ü
c => ü
h => |
i => |
j => |
o => |
p => ü
q => ü
r => ü
s => ü
1 => ð
2 => ð
3 => ð
7 => |
8 => ð
9 => ð
A => ü
B => ü
C => ü
O => p
P => Œ
Q => Π|
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RayJones
Joined: 20 Aug 2008
Posts: 30
Location: Melbourne, Australia
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| Posted: Sat Nov 22, 2008 8:15 pm |
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Is this a simple human interactive test program?
The reason I ask is you are responding with 8 characters for a single received character.
You are certain to have a rx overrun since both ports are @ 4800 for a full speed receive operation.
Despite that, are you certain the terminal software on your PC is set to 4800N81 also?
Ray |
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Thoman
Guest
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| Posted: Sat Nov 22, 2008 8:57 pm |
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I have simplified my program hoping to find the problem ... in this form it is just a test program.
For the matter of the baudrate; I have put the same on the HW and SW to be able to send data on one uart (HW) with the terminal, and receive data from the second (SW).
Honestly I have put my entire day on this matter and I'm still not remotely close to find a solution . I'll be grateful for any help!
(But for the moment I'm going to bed because it's 4am in France  )
ps: my terminal is correctly set to 4800N81 since I receive the other characters nicely ( " => " ) |
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RayJones
Joined: 20 Aug 2008
Posts: 30
Location: Melbourne, Australia
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| Posted: Sat Nov 22, 2008 10:24 pm |
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I have experienced problems with occasional corrupt character, as described here http://www.ccsinfo.com/forum/viewtopic.php?t=35733.
But your corruption really looks like the bit rate is not being set correctly due to the pattern associated with the characters you send back, and the input you have sent.
I'd hazard a guess that you have a x4 error, and this may be related to the x4 PLL operation....
Have you tried simply a looping back with the same UART before trying the crossover from HW to SW? |
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Ttelmah
Guest
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| Posted: Sun Nov 23, 2008 3:59 am |
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Obvious comment does apply. Do you really have a 9.5MHz crystal?. An 'odd' frequency, and if this is wrong, it'd exaplin everything.
Best Wishes |
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Thoman
Guest
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| Posted: Sun Nov 23, 2008 7:05 am |
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In fact I have a 10MHz crystal; but with the PLL activated the frequency isn't right, I had to adjust it a bit.
By the way I have removed the PLL to test, but it's the same ... The HW give just crap and the soft is ok |
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RLScott
Joined: 10 Jul 2007
Posts: 465
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| Posted: Sun Nov 23, 2008 9:48 am |
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| Thoman wrote: | In fact I have a 10MHz crystal; but with the PLL activated the frequency isn't right, I had to adjust it a bit.
By the way I have removed the PLL to test, but it's the same ... The HW give just crap and the soft is ok |
Here is a way to verify the hardware baudrate settings. Go into a tight loop sending the character '@' over and over. This character is very easy to decode on a scope. Then look at the signal on the scope to see how long the character is. Each character is 10 bit times (assuming 8 bits, 1 stop bit). If you don't have a scope, or you don't trust the sweep calibration of your scope, then do this, which can be much more accurate: As you send out characters at full speed, count the characters and toogle a separate diagnostic output (perhaps on an LED) every 4000 characters. Use a stopwatch to measure the length of time for so many toggles (about 1 minute). Calculate baud rate from that. If you want more accuracy, count for 5 minutes.
_________________
Robert Scott
Real-Time Specialties
Embedded Systems Consulting |
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Ttelmah
Guest
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| Posted: Sun Nov 23, 2008 1:53 pm |
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The 'odds' are that if the PLL is giving the wrong frequency, it is because the crystal is a little overdriven. The PLL on older chips, was extremely sensitive to this. On latter chips it is better, but will still exhibit problems if the crystal is significantly overdriven.
You really should fix this first. I'd try adding a 100R in series with the crystal, and get your frequency right, before trying to chase more complex problems.
Best Wishes |
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