concatenating 4 bytes into one pseudo 32 bit counter?

[HankMcSpank]

So having read up about DDS to get sufficient frequency accuracy, it seems most people typically use a 24 bit or 32 bit accumuator.

Every interrupt a fixed number/value is added to the number held in the accumulator - the accumulator is basically a 32 bit counter.

Can this be kludged in picbasic - concatenate 4 bytes into one 'pretend' 32 bit counter - then add a fixed value to it everytime an interrupt happens?

Here's what one guy does in his assembly interrupt routine for a 16f628 PIC (original source - http://www.g4jnt.com/PIC_DDS.zip )...

ints   ;Using  divide by  prescalar,  Interupt service runs at at Fosc / 200
   ; when set to count 25 before overflowing, ie  every 50 clocks = sampling rate
      bcf     INTCON , T0IF   ;reset the interrupt flag
        bsf TESTSTRB        ;Spare instruction needed to make up 8 clocks total, up to the point of reloading TMR0
    ;So use it to pulse a test point
        movlw   d'235'          ; Load in value to count up to 256 FROM (= NNN) 
        movwf   TMR0            ;Timer restarts counting 2 cycles after here.
                                ;Up to this point takes 8 clocks from Interrupt trigger
                                ;So NNN = 256 - [Wanted count] + 8 / Prescale  
    ;  ie =   256 - 25 + 8 / 2 = 235
 
 ;Below here is not time-critical, but must be less than than about 42 clocks total
 ;   so the whole interrupt takes < 50 clocks and doesn't overrun.
 movf D3, W  ;First output the D/A value from the LAST pass though so there is
 call SineTable ;   no jittering due to variable timing of the addition routine
 movwf PORTB
 movf F0, W  ;Now add the frequency data stored in F3/2/1/0 to D3/2/1/0
 addwf D0
 btfss STATUS, C ;Add lowest order byte and check for and carry at each stage
 goto Add1Done ;  that could ripple right through to MS byte
 incf D1
 btfsc STATUS, Z
 incf D2
 btfsc STATUS, Z
 incf D3
Add1Done
 movf F1, W  ;Add the next byte
 addwf D1
 btfss STATUS, C
 goto Add2Done
 incf D2
 btfsc STATUS, Z
 incf D3
Add2Done   
 movf F2, W  ;... and the next
 addwf D2
 btfsc STATUS, C
 incf D3 
 movf F3, W  ;MS Byte now added in.  If it has overflowed, its is exactly what we want
 addwf D3  ;D0-3 are now updated ready for next pass through, with D3 only sent to D/A converter.
OutInt
 bcf TESTSTRB ;Reset the Test Point 
 retfie   ;This  interrupt takes a max of 35 clocks for worst case addition, so does leave 
    ;  a bit of scope for extra tasks or faster sampling.

....it doesn't mean a lot to me, but the gist of it seems to be add the fixed number to the lowest byte, then when that byte fills up, add a 'carry bit' to the second byte of the four ....rinse repeat until the the whole 32 bits are full, then start again from zero.

If it can be donekludged in Picbasic, would anyone be gracious enough to get me started?!!

If it can't be done, I guess I could try and work out what bits of his code to put in PICBasic ASM interrupt plus other supporting code! (that'll be me gone for a few months!)