Electronic – How to improve the LED display code so that it reacts in real time

assemblymicrochipmicrocontrollerperformancepic

This is a carry on question from my previous one and I was wondering how I can go about improving my code, which currently has an extreme delay in outputting the numbers to the display and also not showing the expected outputs under all situations, i.e., some segments are not lit up.

Please see the images below!

Correct but delayed output 1

Correct but delayed output 2

Correct but delayed output 3

Incorrect and delayed output

From an inexperienced point of view, I imagine that it's a timing issue. But, how I go about solving it isn't quite clear to me at the moment. Therefore, any insights or proposed numbers that I can use will be very much appreciated.

The working code with the ADC code block is below:

LIST        p=16f1829   ;list directive to define processor
#INCLUDE    <p16f1829.inc>  ;processor specific variable definitions

__CONFIG _CONFIG1, (_FOSC_INTOSC & _WDTE_OFF & _PWRTE_OFF & _MCLRE_OFF & _CP_OFF & _CPD_OFF & _BOREN_ON & _CLKOUTEN_OFF & _IESO_OFF & _FCMEN_OFF);
__CONFIG _CONFIG2, (_WRT_OFF & _PLLEN_OFF & _STVREN_OFF & _LVP_OFF);

;-------------------------------------------------------------------------
; UDATA_SHR declares a section of shared (all across the banks) uninitialised data
INT_VAR     UDATA_SHR   ; INT_VAR is the section name in ACCESS RAM
TempC       RES     1   ;
L0          RES     1   ;
w_temp      RES     1   ; variable used for context saving
pclath_temp     RES 1   ; variable used for context saving
status_temp RES     1   ; variable used for context saving

;-------------------------------------------------------------------------

LEDtrisA    EQU     TRISA
LEDtrisC    EQU     TRISC
LEDlatA     EQU     LATA
LEDlatC     EQU     LATC

;-------------------------------------------------------------------------

RESET_VECTOR    CODE    0x0000
    GOTO    START   ; When using debug header, ICD2 may not stop
                    ; on instruction 0 during reset.

;-------------------------------------------------------------------------

INT_VECTOR      CODE    0x0004  ; Interrupt vector location

ISR             ; Relocatable Interrupt Service Routine
                ;   Context saving for ISR
    MOVWF   w_temp      ; save off current W register contents
    MOVF    STATUS, w   ; move status register into W register
    MOVWF   status_temp ; save off contents of STATUS register
    MOVF    PCLATH, w   ; Saves value in register PCLATH
    MOVWF   pclath_temp

;-------------------------------------------------------------------------

;   If the interrupt came from the timer, execute the TMR0 interrupt 
;   service routine. 

    BANKSEL     TMR0
    MOVLW       .96
    MOVWF       TMR0
    BTFSC       INTCON, TMR0IF  
    CALL        Service_TMR0    
    BRA         UpdateDisplay   ; Refresh the display

UpdateDisplay
    BANKSEL     LATA        ; Selects memory bank containing LATA register 
    MOVF        LEDlatA, w  ; display status -> w register
    ANDLW       0x0f        ; Separate the lower half byte
    MOVWF       TempC       ; Save display status in TempC
    BSF         TempC, 4    ; Beginning status of LSD display
    RRF         TempC, F    ; Set the status of the next display
    BTFSS       STATUS, C   ; C = 1?
    BCF         TempC, 3    ; If not, turn off the LSD display
    BTFSC       TempC, 0

    BRA         UpdateMsd   ; If it is turned on, display the MSD
                        ; digit of the number
UpdateLsd
    BCF         TempC, 3    
    BSF         TempC, 1                
    BTFSS       STATUS, Z   ; If it is, skip
    MOVF        L0, w       ; Third LSD digit -> w
    ANDLW       0x0f        ;   /
    BRA         DisplayOut  ; Show it on the display

UpdateMsd
    SWAPF   L0, w       ; MSD figure - >
    ANDLW   0x0f        ;   /
    BTFSC   STATUS, Z   ; MSD = 0?
    MOVLW   0x0a        ; If it is, skip

DisplayOut
    CALL    LedTable    ; Take the mask for a digit
    MOVWF   LEDlatC     ; Set the mask on port B
    MOVF    TempC, W    ; Turn on displays
    MOVWF   LEDlatA
    BRA ISR_END

;-------------------------------------------------------------------------
ISR_END
;   Restore contents before returning from interrupt    
    MOVF    pclath_temp,w   ; PCLATH is given its original content
    MOVWF   PCLATH
    MOVF    status_temp,w   ; STATUS is given its original content
    MOVWF   STATUS
    SWAPF   w_temp,f        ; W is given its original content
    SWAPF   w_temp,w

    BSF     INTCON,GIE  ; Global interrupt enabled
    RETFIE              ; Return from interrupt routine

;-------------------------------------------------------------------------
; LOOKUP TABLE
;-------------------------------------------------------------------------

LUT_VECTOR  CODE    0x0030  ; Lookup Table location

LUT                         ; Lookup table is at the top of third page, 
                            ; but can be placed at some other place, it
                            ; is important to have it all on one page

LedTable
        ADDWF       PCL, F
        RETLW       B'00111111' ; mask for digit 0
        RETLW       B'00000110' ; mask for digit 1
        RETLW       B'01011011' ; mask for digit 2
        RETLW       B'01001111' ; mask for digit 3
        RETLW       B'01100110' ; mask for digit 4
        RETLW       B'01101101' ; mask for digit 5
        RETLW       B'01111101' ; mask for digit 6
        RETLW       B'00000111' ; mask for digit 7
        RETLW       B'01111111' ; mask for digit 8
        RETLW       B'01101111' ; mask for digit 9
        RETLW       B'01110111'
        RETLW       B'01111100'
        RETLW       B'00111001'
        RETLW       B'01011110'
        RETLW       B'01111101'
        RETLW       B'01110001' 
        RETLW       B'00000000' ; no digit ......   

;-------------------------------------------------------------------------

MAIN_PROG   CODE

START

;-------------------------------------------------------------------------

    ERRORLEVEL -302     ; Disable warning accessing register not in bank 0
    BANKSEL OSCTUNE     ; Configure OPTION_REG and TMR0
    MOVLW   0x00        ; Set oscillator to factory calibrated frequency
    MOVWF   OSCTUNE     ;
    BANKSEL STATUS
    ERRORLEVEL +302     ; Enable warning accessing register not in bank 0

CLEAR_RAM                   ; code sequence initialises all GPR's to 0x00   
    MOVLW       0x70        ; initialise pointer
    MOVWF       FSR0        ; to RAM
    CLRF        FSR0H

NEXT
    CLRF        INDF0       ; Clear INDF0 register
    INCF        FSR0L, F    ; Inc pointer
    BTFSS       FSR0L, 7    ; All done?
    GOTO        NEXT        ; No, clear NEXT

CONTINUE                    ; Yes, CONTINUE
    NOP

 ;-------------------------------------------------------------------------
; MAIN BODY OF PROGRAM
;-------------------------------------------------------------------------

; Setup main init
    BANKSEL     OSCCON      ; Selects memory bank containing OSCCON register 
    MOVLW       b'01011000'     ; Set CPU clock speed of 500KHz -> correlates to (1/(500K/4)) for each instruction
    MOVWF       OSCCON          ; OSCCON <- 0x38

; Configure the ADC/Potentimator
                            ; Already in bank1
    MOVLW   b'00001101'     ; Select RA4 as source of ADC and enable the module (careful, this is actually AN3)
    MOVWF   ADCON0
    MOVLW   b'00010000'     ; Left justified - Fosc/8 speed - vref is Vdd
    MOVWF   ADCON1
    BANKSEL ANSELA          ; Selects memory bank containing ANSELA register 
    
; Setup pins as digital I/O 
    MOVLW   0x10        ; Selects memory bank containing ANSELA register 
    ANDWF   ANSELA      ; All pins are digital
    CLRF    ANSELC

; Configure the input & output pins 
    BANKSEL     TRISA           ; Selects memory bank containing TRISA register 
    MOVLW       b'11111100'     ; RA0 and RA1 are configured as outputs and
                            ; used for 7-segment display multiplexing
                            ; RA2 is input push-button for initialization
    MOVWF       TRISA
    CLRF        LEDtrisC    ; Port C is output


    BANKSEL     LATA        ; Selects memory bank containing LATA register 
    CLRF        LEDlatA     ; Set all outputs to "0"
    CLRF        LEDlatC ;
    BSF         LEDlatA, 1  ; Turn on MSD display 

; Setup Timer0 as the delay
    BANKSEL     OPTION_REG
    MOVLW       b'10000100'     ; TMR0 is incremented each 32us (Fclk=8MHz)
    MOVWF       OPTION_REG  ; ps = 32

    BANKSEL     TMR0        ; Selects memory bank containing TMR0 register
    BSF         INTCON, GIE     ; Global interrupt enabled
    BSF         INTCON, TMR0IE  ; Timer TMR0 interrupt enabled

MAINLOOP
    BRA         MAINLOOP    ; Continue forever

A2D:
; Start the ADC
    NOP                     ; Requried ADC delay of 8uS => (1/(Fosc/4)) = (1/(500KHz/4)) = 8uS
    BANKSEL     ADCON0      ; Selects memory bank containing ADCON0 register 
    BSF         ADCON0, GO      ; Start the ADC
    BTFSC       ADCON0, GO      ; This bit will be cleared when the conversion is complete
    GOTO        $-1             ; Keep checking the above line until GO bit is clear

; Grab Results and write to the LEDs
    SWAPF       ADRESH, w       ; Get the top 4 MSbs (remember that the ADC result is LEFT justified!)
    MOVWF       L0
    RETURN

; TIMER 0 Interrupt routine clears the TMR0 interrupt flag.
Service_TMR0:
    BANKSEL     INTCON
    BCF         INTCON, TMR0IF  ; MUST ALWAYS clear this in software or else stuck in the ISR forever
    BTFSC       LATA, 1     ; Check if ADC value already determined
    CALL        A2D             ; Get the ADC result
    RETURN          

;-------------------------------------------------------------------------
; END OF PROGRAM
;-------------------------------------------------------------------------

    END         ; End of program

Best Answer

The answer to this question can be found at the following link to stackoverflow, where the same question was asked.

Related Solutions

How to set the condition code in assembly language

I'm not acquainted with the PIC microcontroller, so I'll give a more general answer. (edit: PIC-specific answer added at the bottom of this post)

Especially smaller microcontrollers, like 8-bit and their derivatives, are limited in what they can do in a single instruction. An instruction may contain the target address for a jump, but not two of them, so then-else is out. You only have the if-then part, but that's enough. There are two approaches. Some controllers let you jump to a given address if a condition is met, others only let you skip the next instruction. In the former case your code will look as follows:

              if-test-succeeds goto test-success
test-failed   first instruction of `else` block
              ...
              goto continue
test-success  first instruction of `then` block
              ...
continue      first instruction after if-then-else

If you can only skip the next instruction you'll write something like

              if-test-succeeds skip next instruction
              goto test-failed
test-success  first instruction of `then` block
              ...
              goto continue
test-failed   first instruction of `else` block
              ...
continue      first instruction after if-then-else

The test itself has also limited possibilities. Like you can't pass two numbers to compare them. What you do is load the accumulator with the first number and in the next instruction subtract the second number. This will cause condition codes like the zero and carry flags to be set/cleared. Conditional instructions will test for those flags. So if you want to write if A = B then do-equal else do-not-equal this would become

              load accumulator with A
              subtract B from accumulator
              if zero-flag set goto do-equal
do-not-equal  first instruction of `else` block
              ...
              goto continue
do-equal      first instruction of `then` block
              ...
continue      first instruction after if-then-else

Important: the instruction set manual will tell you which condition codes will be affected by a given instruction. For instance, in the Z80 the ld instruction (for "load accumulator") will not change any flags. So here loading the accumulator is not sufficient to determine if the data is zero.

edit
OK, so I did some research and I found the following:
The PIC has only 2 conditional jump instructions, BTFSS and BTFSC.

BTFSS: Bit Test F, Skip if Set
Syntax: BTFSS f,b
where f is a register [0..127]
and b is the bit in that register to be tested [0..7]
Description: If bit in register is 0 the next instruction is executed. If the bit is 1 the next instruction is discarded and a NOP is executed instead.

BTFSC: Bit Test F, Skip if Clear
Syntax: BTFSC f,b
where f is a register [0..127]
and b is the bit in that register to be tested [0..7]
Description: If bit in register is 1 the next instruction is executed. If the bit is 0 the next instruction is discarded and a NOP is executed instead.

Electronic – how to display current time

No ATmega32 AVR has an RTC/calendar built into it AFAICS.

Assuming that the reference is to an external battery backed RTC on the AVR board, there isn't any source for the current time on a board without an RTC chip. At best, the bootloader you use with the microcontroller may keep data on many milliseconds have elapsed since the board was powered on - within the tolerance of the clock source and allowing for any occasional missed timer interrupts.

If you do have an RTC chip configured on the board, with the correct time set up on it, there might be a suitable RTC library for that chip. Such a library would typically provide hour(), minute(), second() and other time retrieval methods for your code to use.

The generic time.h C header does not ship with, and therefore is not supported by, AVRdude or Arduino, apparently.

There is a good tutorial on using AdaFruit's RTC breakout board, here.

Best Answer

Related Solutions

How to set the condition code in assembly language

Electronic – how to display current time

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