18F2580 with strange behaviour when using Hserin and RX interrupt

PaulMaker — Sun, 15 Feb 2026 15:48:54 GMT

Hi guys,

I'm facing a weird behaviour with my 18F2580 using Hserin and RX interrupts and I was hoping someone could help.

I'm trying to run a code that when an incoming 2 characters is received, it triggers the interrupt and reads the message.
Once it reads the message, it goes back the the main routine.

The issue is that, once it is turned on, it does not show the correct characters being sent.
However, the interrupt trigger is being done and once it reads the message, goes back to the main routine.

But if I send a long message, from that point on, it will show the correct characters being sent but no longer goes back to the main routine!

Not sure why it does not show the correct message in the first place and also, can't understand why it fails to jump from the interrupt routine back to the main routine!

The message is being sent via bluetooth with a BT module connected directly to the MCU.
The TX from the MCU is disabled because i only need to receive and not transmit.

I filmed this behaviour which can be seen in the link below.

This is the code:

Code:



'****************************************************************

'*  Name    : IC_3_COMTEST2.PBP                                 *

'*  Author  :                                                   *

'*  Notice  : Copyright (c) 2024 [select VIEW...EDITOR OPTIONS] *

'*          : All Rights Reserved                               *

'*  Date    : 19/12/2024                                        *

'*  Version : 1.0                                               *

'*  Notes   : 18F2580 MCU                                       *

'*          :                                                   *

'****************************************************************

'

;----[18F2580 Hardware Configuration]-------------------------------------------

#IF __PROCESSOR__ = "18F2580"

  #DEFINE MCU_FOUND 1

#CONFIG

  CONFIG  OSC = IRCIO67      ; Internal oscillator block, port function on RA6 and RA7

  CONFIG  FCMEN = ON        ; Fail-Safe Clock Monitor ENABLED

  CONFIG  IESO = OFF         ; Oscillator Switchover mode disabled

  CONFIG  PWRT = OFF         ; PWRT disabled

  CONFIG  BOREN = OFF        ; Brown-out Reset disabled in hardware and software

  CONFIG  BORV = 3           ; VBOR set to 2.1V

  CONFIG  WDT = ON           ; WDT ENABLED (control is placed on the SWDTEN bit)

  CONFIG  WDTPS = 512        ; 1:512

  CONFIG  PBADEN = OFF       ; PORTB<4:0> pins are configured as digital I/O on Reset

  CONFIG  LPT1OSC = OFF      ; Timer1 configured for higher power operation

  CONFIG  MCLRE = OFF        ; RE3 input pin enabled; MCLR disabled

  CONFIG  STVREN = OFF        ; Stack full/underflow will NOT cause Reset

  CONFIG  LVP = OFF          ; Single-Supply ICSP disabled

  CONFIG  BBSIZ = 1024       ; 1K words (2K bytes) boot block

  CONFIG  XINST = OFF        ; Instruction set extension and Indexed Addressing mode disabled (Legacy mode)

  CONFIG  DEBUG = OFF        ; Background debugger disabled, RB6 and RB7 configured as general purpose I/O pins

  CONFIG  CP0 = OFF          ; Block 0 (000800-001FFFh) not code-protected

  CONFIG  CP1 = OFF          ; Block 1 (002000-003FFFh) not code-protected

  CONFIG  CP2 = OFF          ; Block 2 (004000-005FFFh) not code-protected

  CONFIG  CP3 = OFF          ; Block 3 (006000-007FFFh) not code-protected

  CONFIG  CPB = OFF          ; Boot block (000000-0007FFh) not code-protected

  CONFIG  CPD = OFF          ; Data EEPROM not code-protected

  CONFIG  WRT0 = OFF         ; Block 0 (000800-001FFFh) not write-protected

  CONFIG  WRT1 = OFF         ; Block 1 (002000-003FFFh) not write-protected

  CONFIG  WRT2 = OFF         ; Block 2 (004000-005FFFh) not write-protected

  CONFIG  WRT3 = OFF         ; Block 3 (006000-007FFFh) not write-protected

  CONFIG  WRTC = OFF         ; Configuration registers (300000-3000FFh) not write-protected

  CONFIG  WRTB = OFF         ; Boot block (000000-0007FFh) not write-protected

  CONFIG  WRTD = OFF         ; Data EEPROM not write-protected

  CONFIG  EBTR0 = OFF        ; Block 0 (000800-001FFFh) not protected from table reads executed in other blocks

  CONFIG  EBTR1 = OFF        ; Block 1 (002000-003FFFh) not protected from table reads executed in other blocks

  CONFIG  EBTR2 = OFF        ; Block 2 (004000-005FFFh) not protected from table reads executed in other blocks

  CONFIG  EBTR3 = OFF        ; Block 3 (006000-007FFFh) not protected from table reads executed in other blocks

  CONFIG  EBTRB = OFF        ; Boot block (000000-0007FFh) not protected from table reads executed in other blocks

#ENDCONFIG





#ENDIF





;----[Verify Configs have been specified for Selected Processor]----------------

;       Note: Only include this routine once, after all #CONFIG blocks

#IFNDEF MCU_FOUND

  #ERROR "No CONFIGs found for [" + __PROCESSOR__ +"]"

#ENDIF





'*****************************************************************************





OSCCON =%01110010 '8MHz INTOSC 

OSCTUNE=%01000000 '





DEFINE OSC 8





'*****************************************************************************





INCLUDE "ALLDIGITAL.pbp"

DEFINE SHOWDIGITAL 1





'*****************************************************************************





Define HSER_BAUD 9600

DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive

'DEFINE HSER_TXSTA 24h ' Enable transmit, BRGH = 1

DEFINE HSER_SPBRG 12  ' 

DEFINE HSER_CLROERR 1 ' Clear overflow automatically

'DEFINE HSER_CLEAR = On









RXBYTE  VAR BYTE

RXFLAG  VAR BIT

RX1 VAR BYTE

RX2 VAR BYTE

RX3 VAR BYTE

RX4 VAR BYTE

RX5 VAR BYTE

RX6 VAR BYTE









CT                        VAR                BYTE

CT2                        VAR                BYTE





INTFLAG                VAR                BYTE

MOODCHANGE        VAR                WORD





'PIE1.5 = 1              ' RCIE

INTCON = %11000000      ' GIE + PEIE





'*****************************************************************************





PORTA=%00000000

PORTB=%00000000

PORTC=%00000000





TRISA=%00000000                                

TRISB=%00000000

TRISC=%10000000   'RC7 - RX pin as input





'*****************************************************************************

'PORTS & PINS 





A0                  VAR  PORTA.0   '

A1                  VAR  PORTA.1   '

A2                  VAR  PORTA.2   '

A3                  VAR  PORTA.3   '

A4                  VAR  PORTA.4   '

A5                  VAR  PORTA.5   '

A6                  VAR  PORTA.6   '

LED1                VAR  PORTA.7   '





B0                  VAR  PORTB.0   '

B1                  VAR  PORTB.1   '

B2                  VAR  PORTB.2   '

B3                  VAR  PORTB.3   '

LED2                VAR  PORTB.4   '

B5                  VAR  PORTB.5   '

B6                  VAR  PORTB.6   '

B7                  VAR  PORTB.7   '





C0                  VAR  PORTC.0   '

C1                  VAR  PORTC.1   '

C2                  VAR  PORTC.2   '

C3                  VAR  PORTC.3   '

C4                  VAR  PORTC.4   '

C5                  VAR  PORTC.5   '

IC_TX               VAR  PORTC.6   'TX HARDWARE PIN / Not Used as TX

IC_RX               VAR  PORTC.7   'RX HARDWARE PIN





INCLUDE "modedefs.bas" 





'[DISPLAY SETTINGS]*****************************************************************************





char var byte

x    var byte  

y    var byte    

BUFF VAR BYTE[16]





;use this define for hw i2c 

'#define hwi2c 1 





;set and uncomment these to use softi2c

SCL var PortA.6      ' I2C Clock

SDA var PortC.0      ' I2C Data





;set these  to match display

ssdheight con 3      ; 7 = 8 PAGES  64*128 ,  3 = 4 pages 32*128

ssdwidth  con 127    ; 128 PIXELS WIDE

sdd1306_addr con $78

Include "ssd1306_I2C.INC"  ' bring it in

include "font7x5_18.bas"





'[INTERRUPT SETTINGS]*****************************************************************************









INCLUDE "DT_INTS-18.bas"

INCLUDE "ReEnterPBP-18.bas"





ASM

INT_LIST  macro    ; IntSource, Label, Type, ResetFlag?

    INT_Handler   RX_INT, _RxISR,   PBP,  yes

    ENDM

    INT_CREATE

    INT_ENABLE    RX_INT  ;enables external (INT) interrupts

ENDASM





'*****************************************************************************





'wsave var byte $20 system ;location for W if in bank0

'wsave var byte $70 system ;location for W if in bank0

'..... If any of these next three lines cause an error ...Comment them out to fix the problem...

'............which variables are needed, depends on the chip you are using.......

wsave1 var byte $A0 system ;location for W if in bank0

wsave2 var byte $120 system ;location for W if in bank0

wsave3 var byte $1A0 system ;location for W if in bank0

        

'[INIT]*****************************************************************************





INIT:





clear





PORTB=%00000000





BIG_TEXT = 0





PAUSE 1000





high led1

high led2

pause 500

low led1

low led2





PAUSE 500





gosub glcd_init

GLCD_CLR

ARRAYWRITE BUFF,["INIT OK",0]

GLCDSTR  0,0,BUFF





PAUSE 500





goto main





'[MAIN ROUTINE]*****************************************************************************





main:





gosub glcd_init

GLCD_CLR

ARRAYWRITE BUFF,["WAITING",0]

GLCDSTR  0,0,BUFF





toggle LED1





pause 1000





gosub calculat





goto main





'[INTERRUPT ROUTINE]*****************************************************************************





RxISR:









HSERIN [RX1, RX2, RX3, rx4]





'ASCII TO DECIMAL CONVERSION

rx1 = (rx3 - "0") * 10

rx1 = rx1 + (rx4 - "0")





gosub glcd_init

GLCD_CLR

ARRAYWRITE BUFF,["RX1= ", dec RX1,0]

GLCDSTR  0,0,BUFF





PAUSE 1000





@ INT_RETURN





'[CONFIRMATION ROUTINE]*****************************************************************************





calculat:









if RX1=57 then





gosub glcd_init

GLCD_CLR

ARRAYWRITE BUFF,["GOOD DATA RECEIVED",0]

GLCDSTR  0,0,BUFF





PAUSE 500

high led2

PAUSE 5000

LOW led2





endif









return





'*****************************************************************************

end

Link for the video showing how it behaves:
https://www.canva.com/design/DAHBZ6V...ce=sharebutton

Thanks in advance for any tips on how to get this code working as it is supposed to.

MEL PICBASIC Forum - PBP3

18F2580 with strange behaviour when using Hserin and RX interrupt