USART Stops Receiving Characters

Hi,

Im having a problem where the usart sucessfully receives characters for a few seconds, each time sending a response, however inevitably stops receiving characters after a while (Interrupt is not triggered, and RCIF doesn't get set). I have set DEFINE HSER_CLROERR 1. The PIC is connected to the computer via a wireless serial link using an XBee, should the 3.3v serial ouput from this module be cause for concern? If I connect the Tx and Rx lines together I get everything i send echo'd back. There is <5mA ripple on the serial and power supply lines. Any ideas?

Edit: Might also be worth noting that the PIC continues to run, for instance it can still HSEROUT while not receiving any serial input.

Edit2: It appears not to stop receiving characters if the oscilloscope probe is connected, does that sound right? It is listed as a 10MOhm, 33pF probe.

Regards,
Daniel

Any scheme to post here?
PIC #
Osc Type and speed, crystal

<img src="http://www.mister-e.org/Pics/CrystalBall_Informations.gif">

Quote:

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Originally Posted by mister_e

Any scheme to post here?
PIC #
Osc Type and speed, crystal

---

It is good to see that it is not only me still using traditional ways, even very ancient ways, to find answers.

But Steve, may be your CrystalBall have limited data base.

I use the Genie in the picture and I get anything I ask her!
The bad thing is that I can only ask three questions per weekend!



----------------------------------

time for a change :D

Just ask here to have more than 3/week... it's still a wish ;)

PIC18F2525 running at 20Mhz with a ceramic resonator.

The Rx line is fed directly from the XBee Tx, Tx (if relevent) goes through a voltage divider to give 3.3v input to the XBee..

Initialisation:
<code>
DEFINE OSC 20

' ---- Setup Hardware for USART ----
DEFINE HSER_BAUD 9600
DEFINE HSER_RCSTA 90h
DEFINE HSER_TXSTA 24h
DEFINE HSER_CLROERR 1

' ---- Setup Hardware for ADC ----
DEFINE ADC_BITS 8 ' Set number of bits in result
DEFINE ADC_CLOCK 3 ' Set clock source (rc = 3)
DEFINE ADC_SAMPLEUS 20 ' Set sampling time in microseconds

INCLUDE "variables.bas" 'Define Variables

' ---- Initialisation ----
Init:
Pause 10 'Safe Start Up Delay

ADCON1 = 14 ' All pins are digital, except AN0 (RA0)
CMCON = 7 ' Turn off comparators
INTCON2.7 = 1 ' Turn off PORT B pull ups

'Timer 0 is used for Input Pulse Measurement
TMR0L = 0 'clear Timer 0 low byte
T0CON = %11000101 'prescale = /64
INTCON.5 = 0 'disable TMR0 interrupt

'Timer 1 is used for the internal game clock
T1CON.4 = 1
T1CON.5 = 1 '8 prescaler
TMR1ON = 0 'Stop the timer, enable once game running

'Timer 2 is used for HPWM, is it really?

Init_Ports:
TRISA = %00000000
TRISB = %00000000
TRISC = %00000000

PORTA = %00000000
PORTB = %00000000
PORTC = %00000000

Input Rx
Output Tx

Input Serial_In
Input Menu
Input Battery
Input Mercury

'No PWM output when pin is input
Input Backlight
HPWM 1,50,40000

Output Serial_Out
Low Serial_Out
Init_Proceedure:

For i = 0 To 200
Pause 1
Next i

GoSub Update_LED
GoSub Update_LCD

HSEROUT ["+"]

Init_Interrupts:
RCIE = 1 'Enable USART Rx Interrupt
TMR1IE = 1 'Enable Timer 1 Interrupt
INTCON2.6 = 0 'INT0 on Falling Edge
INTCON = %11010000 'Global, Peripheral, INT0 Enable

ON Interrupt Goto Interrupt_Handler

Main_Loop:

If Menu Then
Input Backlight
Else
Output Backlight
EndIf

'Motion, Report If Requested.
If (Report_Mercury = 1) AND (Status_Mercury <> Mercury) Then
Report_Mercury = 0
Status_Mercury = Mercury

HSEROUT ["F"]
EndIf

Goto Main_Loop
</code>

Interrupt:
<code>
' ---- Interrupts ----

DISABLE

Interrupt_Handler:
If RCIF Then Goto Int_Rx
If INT0IF Then Goto Int_Hit
If TMR1IF Then Goto Int_Time

Interrupt_Exit:
INT0IF = 0
While RCIF
t = RCREG ' trash leftovers to clear RCIF before return
Wend
RESUME

'-------

Int_Rx:
If RCSTA.1 Then
HSEROUT ["Overrun"]
Pause 6
EndIf

HSERIN 1, Interrupt_Exit, [PacketID, PacketCheckSum, str Buffer\20\Sentinel]
CheckSum = 0

If PacketID > 0 Then
For i = 0 To 20
CheckSum = CheckSum + Buffer[i]
Next i
EndIf

If (PacketID > 0) AND (PacketCheckSum != (255 - CheckSum)) Then 'Failed To Receive Correctly
HSEROUT ["\", PacketID]
Pause 6
Else
Select Case Buffer[0]
'Do Stuff
End Select

Pause 6
HSEROUT ["/", PacketID]
Pause 6
EndIf


Goto Interrupt_Exit
</code>

Does it work if you remove the wireless link and have a direct cable connection?

If not then there is a code problem with the PIC

If it works then for some reason the radio link is dying.

Quote:

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Originally Posted by breesy

PIC18F2525 running at 20Mhz with a ceramic resonator.


INCLUDE "variables.bas" 'Define Variables

</code>

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Hi Breezy,
no one can compile without variables.bas
JS

Hi,

Problem solved with addition of 33pF cap between the line and ground..

I am at a loss to explain why... Could there have been a high frequency ripple that I could not see on the scope since the probe is arresting it?