pulsein question (units of measure?)

[nomad]

I know the resolution for pulsein is determined upon the oscillator frequency, but I thought the unit of measure was in microseconds. yet my code produces 2 different results, leading me to think that resolution is actually the unit of measure. (ie: a pulsein measurement of 250 with a 20mhz crystal is actually 500us?)

@ DEVICE pic16F88, HS_OSC ' osc setting
@ DEVICE pic16F88, WDT_ON  ' Watchdog Timer
@ DEVICE pic16F88, PWRT_ON ' Power-On Timer
@ DEVICE pic16F88, MCLR_OFF ' Master Clear Options (Internal)
@ DEVICE pic16F88, BOD_ON ' Brown-Out Detect
@ DEVICE pic16F88, LVP_OFF ' Low-Voltage Programming
@ DEVICE pic16F88, CPD_OFF ' data protect
@ DEVICE pic16F88, PROTECT_OFF ' code protect

define osc 20

        PORTB = 0
        PORTA = 0
        TRISB = 0
        TRISA = 255
        CMCON = 7
        ADCON0 = 0
        ADCON1 = 0
        ansel = 0
        x var WORD
        FREQ VAR WORD
        w1 var word
        w2 var word
        TEMP VAR WORD
        
             ' Set LCD Data port
	DEFINE LCD_DREG	PORTB
	' Set starting Data bit (0 or 4) if 4-bit bus
	DEFINE LCD_DBIT	4
	' Set LCD Register Select port
	DEFINE LCD_RSREG PORTB
             ' Set LCD Register Select bit
	DEFINE LCD_RSBIT 2
	' Set LCD Enable port
	DEFINE LCD_EREG	PORTB
	' Set LCD Enable bit
	DEFINE LCD_EBIT	0
	' Set LCD bus size (4 or 8 bits)
	DEFINE LCD_BITS	4
	' Set number of lines on LCD
	DEFINE LCD_LINES 2
	' Set command delay time in us
	DEFINE LCD_COMMANDUS 2000
	' Set data delay time in us
	DEFINE LCD_DATAUS 50
        
 LCDOUT $fe,1
    Pause 500       ' Wait for LCD to startup
    Lcdout $fe,1,  "Speed Adjuster"   ' Clear LCD screen start line 1
    LCDOUT $FE,$C0," GIDDYUPGO.NET" ' goto start line 2
    pause 5000
    LCDOUT $FE,1
           
Start:
PULSIN PORTA.1,1,W1
PULSIN PORTA.1,0,W2
X=W1+W2 'period = high + low
TEMP=1000
TEMP=TEMP*TEMP 'get 1000000 for div32
FREQ = DIV32 X 'freq = 1000000 / period(in .us)
lcdout $fe,$80,"FRQ pulse ",#freq
PAUSE 100
count PORTA.1,250,w1
FREQ = W1*4
lcdout $fe,$c0,"FRQ count ",#FREQ
PAUSE 1000
goto start

[dhouston]

The manual gives the units. It varies with the oscillator frequency.

4MHz = 10µS
20MHz = 2µS

which works out to 40/fOsc.

[nomad]

Actually the manual gives the resolution, but does not specify the units of measure.
(I've read the manual)

The resolution of PULSIN is dependent upon the oscillator frequency. If a 4MHz oscillator is used, the pulse width is returned in 10us increments. If a 20MHz oscillator is used, the pulse width will have a 2us resolution. Defining an OSC value has no effect on PULSIN. The resolution always changes with the actual oscillator speed.

they probably could clarify that part a bit.
Thanks for your reply.

Edit: that 40/fOsc should come in handy when I cannot find a standard crystal. ( Have lots of 10.24Mhz etc lying about) Thanks