timer.inc

来自「this asm is for lcd driver」· INC 代码 · 共 52 行

; PRESCL and TIMER computation
	nolist
; Take the processor clock frequency in Hz (clock), and
; the required time delay in uSecs (dusec), and compute
; a value for the prescaler (PRESCL) and another for
; TMR0 (TIMER).

_cycle	equ	clock >> 2
_dfreq	equ	1000000 / dusec
_divr	equ	_cycle / _dfreq
	if (_divr < 512)
	error "Delay time too short. Assign PSA to WDT."
	endif
_test	set	_divr / 256
_testB	equ	_divr % 256
	if (_testB > 0)
_test	set	_test + 1
	endif
	if (_test > 1)
_temp	set	2
PRESCL	set	0
	endif
	if (_test > 2)
_temp	set	4
PRESCL	set	1
	endif
	if (_test > 4)
_temp	set	8
PRESCL	set	2
	endif
	if (_test > 8)
_temp	set	16
PRESCL	set	3
	endif
	if (_test > 16)
_temp	set	32
PRESCL	set	4
	endif
	if (_test > 32)
_temp	set	64
PRESCL	set	5
	endif
	if (_test > 64)
_temp	set	128
PRESCL	set	6
	endif
	if (_test > 128)
	error "Timer requirement is outside range"
	endif
TMRVAL	equ	256 - (_cycle / _temp / _dfreq)
	list