# SXMicrocontrollerDSPMathMethod

## 8bit 16 step Averageing filter by Andrew Warren

```    ; Written by Andrew Warren [fastfwd at ix.netcom.com].
;
;       (NEW - AVE) + 16*AVE
; AVE = --------------------
;               16

NEW	equ	[ANY FILE REGISTER]	;HOLDS NEW SAMPLE [0-255].
AVE	equ	[ANY FILE REGISTER[	;HOLDS THE AVERAGE [0-255].
AVFRAC	equ	[ANY FILE REGISTER]	;HOLDS THE FRACTIONAL PART
;OF THE AVERAGE [0-15].
TEMP	equ	[ANY FILE REGISTER]	;TEMPORARY STORAGE.

FILTER:

mov	W, #00001111B	;MASK OFF ALL BUT THE FRACTIONAL
and	AVFRAC, W	;PART OF THE OLD AVERAGE
;(AVFRAC'S HI-NIBBLE CAN
;CONTAIN GARBAGE).

mov	W, AVE	;NEW = NEW - AVE.
sub	NEW, W	;CARRY = 0 IF THE DIFFERENCE IS
;NEGATIVE, CARRY = 1 IF POSITIVE.

mov	W, <>AVE;HI-NIBBLE OF W = MIDDLE NIBBLE
;OF 16*AVE.

mov	TEMP, W	;LO-NIBBLE OF TEMP = HI-NIBBLE
;OF 16*AVE (LO-NIBBLE OF 16*AVE
;IS ALWAYS 0000).

; NEW CONTAINS (NEW - AVE) AND [TEMP:W] HOLDS 16*AVE.
; ADD THEM TOGETHER.

sb	C	;IF (NEW - AVE) WAS NEGATIVE,
dec	TEMP	;ADJUST THE HI-NIBBLE OF 16*AVE.

and	W, #11110000B	;W = LO-BYTE OF 16*AVE.
or	W, AVFRAC	;(INCLUDE AVE'S FRACTIONAL
;PART).

add	W, NEW	;W = LO-BYTE OF
;((NEW-AVE) + 16*AVE).
;CARRY = 1 IF SUM > 255,
;CARRY = 0 OTHERWISE.

mov	AVFRAC, W	;LO-NIBBLE OF AVFRAC =
;FRACTIONAL PART OF FINAL
;RESULT.  HI-NIBBLE = GARBAGE.

and	W, #11110000B	;W = (LO-NIBBLE OF
;((15*AVE+NEW)/16)) * 16.

mov	AVE, W	;AVE = (LO-NIBBLE OF
;((15*AVE+NEW)/16)) * 16.

swap	AVE	;AVE = LO-NIBBLE OF
;((15*AVE+NEW)/16).

; AVE'S LO-NIBBLE CONTAINS THE LO-NIBBLE OF THE FINAL RESULT.
; AVE'S HI-NIBBLE = 0000.

snb	C	;LO-NIBBLE OF TEMP =
inc	TEMP	;HI-NIBBLE OF ((15*AVE+NEW)/16).

mov	W, <>TEMP	;HI-NIBBLE OF W = HI-NIBBLE OF
and	W, #11110000B	;((15*AVE+NEW)/16).
;LO-NIBBLE OF W = 0000.

; W'S HI-NIBBLE CONTAINS THE HI-NIBBLE OF THE FINAL RESULT.
; LO-NIBBLE = 0000.

or	AVE, W	;COMBINE THE HI- AND LO-NIBBLES
;AND STORE THE FINAL RESULT IN
;AVE.

; AVE CONTAINS THE NEW AVERAGE.

See?  That wasn't too hard; just 20 words of program space and
20 instruction cycles...  And not a single floating-point
operation anywhere in there.
```

 file: /Techref/scenix/lib/math/dsp/av-16w-aw_sx.htm, 3KB, , updated: 2004/6/10 14:40, local time: 2024/4/21 04:13, TOP NEW HELP FIND:  3.238.235.248:LOG IN

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