;******************************************
; Filename:	ledriver.asm *
; Date: August 10, 1999 *
; File Version: *
; *
; Author: Lawrence Foltzer *
; Company: photons unlimited *
;******************************************
; Notes:
;
; Variable amplitude LED drive current pulse generator.
; this code generates a series of "N" pulses to a switching
; power supply that generates a supply voltage high enough
; to operate the laser driver in the avalanche mode.
; The "N" pulses are then followed by a trigger pulse to
; avalanche transistor, which then drive the LED.
; For details on the voltage generated versus the number of
; applied pulses, see the Mathcad file vc_vs_nt.mcd.
; Will use GPIO(0:2) for switcher drive pulses, and GPIO5
; as the avalanche trigger signal port.
; 50nsec pulses to 8 amps are generated.
;******************************************
list p=12c508 ; list directive to define processor
#include  ; processor specific variable definitions
__CONFIG _CP_OFF & _WDT_OFF & _MCLRE_OFF & _IntRC_OSC 
; constants
nn	equ	0x64	; 100 base 10 is number of pulses
delay	equ	0x20
; variable storage
ORG	0x07
cntr	res	1
;**********************************************************************
;	ORG 0x1FF ; processor reset vector
;	movlw	0x80
; Internal RC calibration value is placed at location 0x1FF by Microchip
; as a movlw k, where the k is a literal value.
; pseudocode
; pulse switcher "nn" times
; trigger avalanche driver
; wait a ms or so
; repeat.
ORG	0x000	; coding begins here
movlw	0x80
start	movwf	OSCCAL
movlw	0x80
OPTION
clrf	GPIO
movlw	0x08
tris	GPIO
repeat	movlw	0x32	; 50 pulses please
movwf	cntr
lp1	movlw	0x07
movwf	GPIO	; pulse high
;	nop
;	nop
nop
movlw	0x00
movwf	GPIO	; pulse low
nop
nop
;	nop
decfsz	cntr,1
goto	lp1
movlw	delay
movwf	cntr
w8lp1	decfsz	cntr,1
goto	w8lp1
bsf	GPIO,5	; trigger avalanche transistor
bcf	GPIO,5
dec1	decfsz	cntr,1
goto	dec1
movlw	0x64	; 100 pulses please
movwf	cntr
lp2	movlw	0x07
movwf	GPIO	; pulse high
;	nop
;	nop
nop
movlw	0x00
movwf	GPIO	; pulse low
;	nop
nop
nop
decfsz	cntr,1
goto	lp2
movlw	delay
movwf	cntr
w8lp2	decfsz	cntr,1
goto	w8lp2
bsf	GPIO,5	; trigger avalanche transistor
bcf	GPIO,5
dec2	decfsz	cntr,1
goto	dec2
movlw	0x96
movwf	cntr
lp3	movlw	0x07
movwf	GPIO	; pulse high
;	nop
;	nop
nop
movlw	0x00
movwf	GPIO	; pulse low
;	nop
nop
nop
decfsz	cntr,1
goto	lp3
movlw	delay
movwf	cntr
w8lp3	decfsz	cntr,1
goto	w8lp3
bsf	GPIO,5	; trigger avalanche transistor
bcf	GPIO,5
dec3	decfsz	cntr,1
goto	dec3
goto	repeat
ORG	0x01ff
movlw	0x80
END

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