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MikeMcGlade

Mike McGlade

Mike has 16 years of experience with Microchip products including MCU, Memory & Analog.  He also has significant knowledge of lighting, safety & security and vending industries.

 


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  • Hi Mike

     

    I'm having some trouble with a bit of PIC assembly code running on a PIC16F722.  I am trying to use the Timer0 interrupt and the SSP module, in SPI mode.  The SSP module is communicating with an MCP23S17.

    The affected sections of the code are

     

              movlw     0x87                                 ;Put 0x87 in the working register

              movwf     OPTION_REG                   ;Copy the working register to the options register, Port B pull-ups disabled, Timer0 pre-scaler set to 256

     

    and

     

    SPI_Byte_Out:

              bcf          INTCON, GIE                    ;Disable all interrupts while transmitting
              movwf      SSPBUF                         ;Copy the working register to SSPBUF
              bsf          STATUS, RP0                  ;Access memory bank 1
              btfss       SSPSTAT, BF                  ;Check buffer full bit for end of transmission
              goto        $-1                                  ;Go to previous instruction until transmission is complete
              bcf          STATUS, RP0                  ;Access memory bank 0

              bsf          INTCON, GIE                   ;Re-enable all interrupts after transmission

              return

     

    When the first part of the code shown is commented out, or if the GIE bit is cleared, the SSP module functions reliably.  However when this part of the code is included, the SSP module doesn't function properly, with nothing output on the SO pin and the code hanging at the Buffer Full bit test.

    Have your encountered this before, or can you see what I'm doing wrong?

Reply

  • Hi Mike

     

    I'm having some trouble with a bit of PIC assembly code running on a PIC16F722.  I am trying to use the Timer0 interrupt and the SSP module, in SPI mode.  The SSP module is communicating with an MCP23S17.

    The affected sections of the code are

     

              movlw     0x87                                 ;Put 0x87 in the working register

              movwf     OPTION_REG                   ;Copy the working register to the options register, Port B pull-ups disabled, Timer0 pre-scaler set to 256

     

    and

     

    SPI_Byte_Out:

              bcf          INTCON, GIE                    ;Disable all interrupts while transmitting
              movwf      SSPBUF                         ;Copy the working register to SSPBUF
              bsf          STATUS, RP0                  ;Access memory bank 1
              btfss       SSPSTAT, BF                  ;Check buffer full bit for end of transmission
              goto        $-1                                  ;Go to previous instruction until transmission is complete
              bcf          STATUS, RP0                  ;Access memory bank 0

              bsf          INTCON, GIE                   ;Re-enable all interrupts after transmission

              return

     

    When the first part of the code shown is commented out, or if the GIE bit is cleared, the SSP module functions reliably.  However when this part of the code is included, the SSP module doesn't function properly, with nothing output on the SO pin and the code hanging at the Buffer Full bit test.

    Have your encountered this before, or can you see what I'm doing wrong?

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