Intel 80C188EC User Manual page 284

$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
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
mov bp, sp
_space equ word ptr[bp+6]
_mark equ word ptr[bp+8]
push ax
push bx
push dx
mov dx, T1CMPA
mov ax, _mark
out dx, al
mov dx, T1CMPB
mov ax, _space
out dx, al
mov dx, T1CNT
xor ax, ax
out dx, al
mov dx, T1CON
mov ax, C003H
out dx, al
Example 9-2. Configuring a Square-Wave Generator
;substitute register offsets
;save caller's bp
;get current top of stack
;get parameters off the stack
;save registers that will be
;modified
;set mark time
;set space time
;Clear Timer 1 Counter
;start Timer 1
TIMER/COUNTER UNIT
9-21