Intel 80C188XL, 80C186XL Timer/Counter Unit, Example 9-2.Configuring a Square-WaveGenerator

TIMER/COUNTER UNIT

$mod186

name example_timer1_square_wave_code

;FUNCTION: This function generates a square wave of given

;frequency and duty cycle on Timer 1 output pin.

;SYNTAX: extern void far clock(int mark, int space)

;

;INPUTS: mark - This is the mark (1) time.

;space - This is the space (0) time.

;The register compare value for a given time can be

;easily calculated from the formula below.

;

;CompareValue = (req_pulse_width*f)/4

;OUTPUTS: None

;

;NOTE: Parameters are passed on the stack as required by

;high-level Languages

T1CMPA	equ xxxxH	;substitute register offsets
T1CMPB	equ xxxxH
T1CNT	equ xxxxH
T1CON	equ xxxxH
lib_80186	segment public ’code’
assume	cs:lib_80186
public	_clock
_clock	proc far
push	bp	;save caller’s bp
mov	bp, sp	;get current top of stack
_space	equ word ptr[bp+6]	;get parameters off the stack
_mark	equ word ptr[bp+8]
push	ax	;save registers that will be
push	bx	;modified
push	dx
mov	dx, T1CMPA	;set mark time
mov	ax, _mark
out	dx, al
mov	dx, T1CMPB	;set space time
mov	ax, _space
out	dx, al
mov	dx, T1CNT	;Clear Timer 1 Counter
xor	ax, ax
out	dx, al
mov	dx, T1CON	;start Timer 1
mov	ax, C003H
out	dx, al

Example 9-2. Configuring a Square-Wave Generator

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