DT-ints-18, How to ...

[iw2fvo]

I have loaded the program as indicated .
No errors displayed.
I am using pbp 2.50, picf184523 @ 40 MHz speed.
I have a square wave output at porta.4 and 100 msec period ( 50 msec high and 50 msec low ).
Where does the 100 msec come from ?
How could I set different periods ?
The program is attached here.
Thanks
Ambrogio

'HSPLL OSCILLATOR HAS BEEN DEFINED IN THE PBP FOLDER > 18F4523 FILE

DEFINE OSC 40
LED1 VAR PORTA.4
INCLUDE "DT_INTS-18.bas" ' Base Interrupt System
INCLUDE "ReEnterPBP-18.bas" ' Include if using PBP interrupts

ASM
INT_LIST macro ; IntSource, Label, Type, ResetFlag?
INT_Handler TMR1_INT, _ToggleLED1, PBP, yes
endm
INT_CREATE ; Creates the interrupt processor
ENDASM

T1CON = $31 ; Prescaler = 8, TMR1ON
@ INT_ENABLE TMR1_INT ; enable Timer 1 interrupts

Main:
PAUSE 1
GOTO Main

'---[TMR1 - interrupt handler]--------------------------------------------------
ToggleLED1:
TOGGLE LED1
@ INT_RETURN

[Darrel Taylor]

>Where does the 100 msec come from ?

It comes from the formula ...
1/(OSC * 1000000 / 4 / Prescaler / 65536)
1/(40 * 1000000 / 4 / 8 / 65536) = 0.0524 Sec. = 52.4 mS
Times 2 for a full cycle = 104.8 mS

>How could I set different periods ?

If the frequency is fixed, use the Timer Template ...
http://darreltaylor.com/DT_INTS-14/TimerTemplate.html

[Demon]

Do we just change these to their 18F counterparts for 18F PICs?

INCLUDE "DT_INTS-14.bas"
INCLUDE "ReEnterPBP.bas'

Robert

[iw2fvo]

Thanks Darrel for the assistance.
I red the pic18f4523 spec and I am just a little bit confused on how write and read the timer1 counter that is 16 bit long.
What is the picbasic code to read and write that 16 bit timer/counter ?
Your responses are always sharp an relly effective: congratulation.
Best regards,
Ambrogio
IW2FVO

[Dave]

IW2FVO,
To read the timer:

variable var word
variable = tmr1

To write the timer:
tmr1 = variable

Its just that simple....

[iw2fvo]

thanks,
if I write tmr1= 64 then the compiler gives me :
>> error 113..... pbpp18.lib580 : symbol not previously defined (tmr1 ) and then the same message but lib588, lib927, lib 933.
So the point is still : how to read / write TMR1 ?
Any help is appreciated.
Thanks
Ambrogio

[Demon]

Is post #10 above the issue?

Robert

[HenrikOlsson]

Hi,
It's easy but I'm afraid it's not THAT easy - there is no TMR1 register (hence the error). Instead TMR1 consists of TWO 8bit regsiters, TMR1L and TMR1H.

The straight forward way to write it is to do

TMR1L = 0
TMR1H = 0

And the straight forward way to read it is

myVar VAR WORD
myVAR.HighByte = TMR1H
myVAR.LowByte = TMR1L

When reading TMR1 this way there's a slight posibillity that TMR1L overflows right in between reading TMR1H and TMR1L giving you a wrong result. To prevent that the easiest way is to simply STOP the timer before reading it. If that's not possible there are other ways to cater for that - and there are tricks that allows you to read it in one go if needed but lets keep it as simple as possible for now.

/Henrik.

[Darrel Taylor]

If you are using the Timer Template, then there's no reason to read or write to the Timer directly. It is handled for you by the template.

If you are not using the template, you should at least use the Timer Reload routine from the template.
To maintain a constant frequency that also accounts for interrupt latency, the reload value must be ADDED to the current value in the Timer.

Just reloading a value into the Timer will give a frequency output, but accuracy and consistency will suffer.

There are other ways to ADD the reload value to the Timer, but you must know exactly how many instructions it takes to do the addition.
The routine in the template is already known to take 8 instruction cycles.
The template automatically adjusts for that amount of time.

With the template, if you tell it you want 100hz ... you get 100.0 Hz.

With all of that said ... you still haven't revealed whether you want a Fixed frequency or Variable frequencies?
It makes a huge difference.